Date: 202012
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Rain; 3
Light: Night
Aircraft: Small Transport
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Training
Flight phase: Landing
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Taxi
Reporter function: Captain; Check Pilot; Flight Engineer / Second Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Human factors: Time Pressure; Workload
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: Other after rotation
Result: General None Reported / Taken
Contributing factors: Company Policy; Human Factors; Weather
Primary problem: Human Factors

Narrative: Flight originated in ZZZ as a Part 135 scheduled flight to ZZZ1. There were no passengers on board.  ZZZ Center advised us that ZZZ4 Center would be going to an 'ATC Zero' condition for 1 hour 30 minutes at 15 minutes prior to our scheduled arrival due to a COVID situation in the Center facility. I made the decision to divert to ZZZ3 and accomplished training enroute and landing late afternoon. Weather in ZZZ3 was IFR with a report that fog was believed to be moving into the ZZZ3 area. We refueled and departed for ZZZ1. Training was again accomplished enroute...landing was at night with 2;500 broken; 3;100 overcast and 3 mile in R and BR. This was the end of a long day that started early morning for a departure to ZZZ5 from ZZZ1...scheduled time was 1 hour 50 minutes with a 20 minute turn. Due to waiting for a dead heading crew member we left ZZZ5 one hour late; arriving ZZZ1 at noon. I picked up another FO and departed for ZZZ for a planned 1 hour 40 minute flight. Landing at ZZZ; we then departed for a planned 1 hour 40 minute flight to ZZZ1. As noted previously; we were forced to divert to ZZZ3; due to ATC Zero. I exceeded 8 hours but; felt that; per our FOM and the FARs; I was legal to start and finish because the divert to ZZZ3 was not planned and the scheduled times were within legal limits. Note that I had over 14 hours rest before the flying the following day and was off duty after the days flying was complete and no other flying scheduled for several days.The issue that bothers me is that I was accomplishing training at night and in solid IMC conditions...never again. There was some unspoken pressure to get the training accomplished due to approaching holiday and a lack of aircraft to accomplish the training during daylight hours. I also should not have pressed the flying...the start of the problem was the unplanned ZZZ5 turn due to the scheduled Captain timing out and for whom I was asked to cover. As soon as we knew we would have to divert to ZZZ3; I should have terminated any further training and proceeded to ZZZ1 as soon as ZZZ4 Center re-opened. Several 'takeaways'...I will not allow this to happen to me again; even though I believed (and believe) I was legal...fatigue was not an issue. Training should only be accomplished in solid VMC conditions and preferably in daylight.




Synopsis: Air taxi Captain reported a training flight session extended well beyond the original time planned due to a divert caused by an ATC Zero at an enroute Center.