Question: When was the Rob Renzetti the supervising producer for Gravity Falls?

Context paragraphs:
Gravity Falls: Gravity Falls is an American animated television series produced by Disney Television Animation originally for Disney Channel (and then later for Disney XD) from June 15, 2012 to February 15, 2016.

Gravity Falls: Legend of the Gnome Gemulets: Gravity Falls: Legend of the Gnome Gemulets is a platform video game for the Nintendo 3DS, developed and published by Ubisoft and produced by Disney Interactive Studios based on the animated Disney series, "Gravity Falls".  The game utilizes UbiArt Framework engine, and was released on October 20, 2015.

Weirdmageddon 3: Take Back The Falls: "Weirdmageddon 3: Take Back The Falls" is the series finale of the American animated television series "Gravity Falls", created by Alex Hirsch.  The episode was written by Shion Takeuchi, Mark Rizzo, Josh Weinstein, Jeff Rowe, and Hirsch, and directed by Stephen Sandoval.  The series follows twelve-year-old twins Dipper (voiced by Jason Ritter) and Mabel Pines (voiced by Kristen Schaal), who stay for the summer with their grand uncle Grunkle Stan (voiced by Hirsch) in a tourist trap called the Mystery Shack, set within the fictional town of Gravity Falls, Oregon.  In this episode, Ford (voiced by J.K. Simmons) discovers the extent of Bill Cipher's plans, while the Mystery Shack crew forms a plan to fight back and reclaim the town.  A final confrontation with Bill leads to the Pines family's ultimate fate and greatest sacrifice.

List of Gravity Falls episodes: "Gravity Falls" is an American animated series created by Alex Hirsch for Disney Channel, and now for Disney XD.  The series revolves around the various antics of two fraternal twins, Dipper (voiced by Jason Ritter) and Mabel Pines (voiced by Kristen Schaal), who were handed over to their Great Uncle (or "Grunkle") Stan (voiced by Alex Hirsch), who runs a tourist trap called The Mystery Shack, in the town of Gravity Falls, Oregon.  They soon realize that the mysterious town holds plenty of secrets.  When Dipper obtains an old journal that he finds in the forest, they find that their everyday lifestyle changes with odd things and creatures they encounter.

Randy Myers (animator): Randy Myers (born March 29, 1967) is an American Animator and animation director.  He is best known for his animation direction work on "Samurai Jack" and "The Powerpuff Girls".  His other works include "The Grim Adventures of Billy and Mandy", "Foster's Home for Imaginary Friends", "Dexter's Laboratory", "Cats Don't Dance", "The Iron Giant", "My Life as a Teenage Robot", "The Fairly OddParents", "Gravity Falls", "", among others.  He is supervising producer on "We Bare Bears".

Dipper Pines: Mason "Dipper" Pines is a fictional character and one of the main characters of the Disney XD animated series "Gravity Falls".  The character is voiced by Jason Ritter, and designed by and loosely based on the childhood of series creator, Alex Hirsch.  The character first appeared on the unreleased, unnamed pilot created by Hirsch with which he pitched the show; he later appeared on the first episode "Tourist Trapped".  Dipper, along with his twin sister Mabel Pines, stars in every episode of the show.  Dipper is the star of the Gravity Falls series of shorts titled "Dipper's Guide to the Unexplained" and also appears in the shorts "Fixin' it with Soos" and "Mabel's Guide to Life".

Not What He Seems: "Not What He Seems" is the eleventh episode of the second season of the American animated television series "Gravity Falls", created by Alex Hirsch.  The episode was written by Shion Takeuchi, Josh Weinstein, Jeff Rowe, Matt Chapman, and Hirsch, and directed by Stephen Sandoval.  The series follows twelve-year-old twins Dipper (voiced by Jason Ritter) and Mabel Pines (voiced by Kristen Schaal), who stay for the summer with their grand uncle Grunkle Stan (voiced by Hirsch) in a tourist trap called the Mystery Shack, set within the fictional town of Gravity Falls, Oregon.  In this episode, Dipper and Mabel begin to question who Stan really is after officers arrest him for stealing chemical waste.  The episode, which breaks the show's status quo by revealing Stan's brother, ends with a cliffhanger to the second half of the season.

Rob Renzetti: Robert Renzetti (born September 12, 1967) is an American animator and director who created the animated television series "My Life as a Teenage Robot" for Nickelodeon, and directed "Dexter's Laboratory", "The Powerpuff Girls", and "Samurai Jack" for Cartoon Network.  He has also served as story editor for the first two seasons of "", and was supervising producer on the Disney Channel animated series "Gravity Falls".

Big City Greens: Big City Greens (formerly known as "Country Club") is an upcoming Disney animated television series.  The series is created by Chris and Shane Houghton, who originally worked on Nickelodeon's "Harvey Beaks".  Emmy Award-winning director Rob Renzetti (creator of "My Life as a Teenage Robot" and supervising producer for "Gravity Falls") serves as executive producer and the Houghton brothers serve as co-executive producers.  It is scheduled to premiere on Disney XD in 2018.

The Cartoonstitute: The Cartoonstitute was a planned Cartoon Network project created by Cartoon Network's executive Rob Sorcher that would have been a showcase for animated shorts created without the interference of network executives and focus testing.  It was headed by Craig McCracken (creator of "The Powerpuff Girls", "Foster's Home for Imaginary Friends", and "Wander Over Yonder") and Rob Renzetti (creator of "My Life as a Teenage Robot").  39 shorts for the project were in development at Cartoon Network Studios, but only 14 of these were completed.  Eventually, balancing 5 upcoming shows and adding another proved difficult and the project was scrapped.  Of the shorts which were made, only "Regular Show" and "Uncle Grandpa" have been greenlit to become animated series (the latter was initially greenlit as "Secret Mountain Fort Awesome", before becoming a series of its own).  On May 7, 2010, Cartoon Network uploaded nearly all of the shorts to their website.  The only shorts not uploaded were "Maruined", "3 Dog Band", and "Joey to the World".

Supporting paragraphs: Rob Renzetti Gravity Falls
Answer: June 15, 2012 to February 15, 2016