Small Aircraft; High Wing; 1 Eng; Fixed Gear
Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 14; Flight Crew Total 1205; Flight Crew Type 1109
Confusion; Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Environment - Non Weather Related; Human Factors; Aircraft; Procedure
While attempting to talk to Ground and Tower while parked on the north ramp I did not receive any responses back. Listened to ATIS again and heard that the Tower closed each day at XA00.  Checked the time and it was after XA00 Z and continued on as I would with a closed Tower. I taxied to get fuel and continued to make radio calls and then took off.  While in cruise I realized that the radio was not working correctly. After fixing the radio I continued the flight.  While coming back to land at ZZZ I listened to ATIS 8 miles out and noticed that the time now said the tower closes at XA00 local time. I then called the Tower and let them know that I had ATIS and requested to land and was cleared to land and landed with no incident. Contributing factors are a Tower closure during this pandemic times; a radio that was not working correctly; and the XA00 local time vs Zulu time and possibly not identified on ATIS as local time vs. Zulu time on the initial ATIS weather.
Pilot departed airport without communication with Tower. Pilot mistook LOCAL time for ZULU time; and departed the airport when Tower was open.