You cannot place the ampersand  at the end of the original command because when the command is executed it will result in the following:

; /tmp/vPdOv.bin & ; rm -f /tmp/vPdOv.bin ; rm -f /tmp/rFNEC.b64

The ampersand cannot appear just before semicolon as they both serve as command terminators and it will generate an error and break the stager execution.

The sleep was added as "padding" that wouldn't generate any output.  We could shorten the sleep but I figured since it was there the 5 seconds would provide plenty of time for the stager to load and be complete even on very slow systems.