Hi…,
Flight planning and flying in general is done in Universal Coordinated Time (sometimes referred to as Zulu Time) deliberately to avoid the issues of different time zones. Most aircraft have cockpit clocks set to UTC. Try looking at a panel clock in your flight sim with the flight sim time set to real time.
You might like to add UTC to your Windows Clock (bottom right of screen) so you have UTC ready and can see how UTC compares to your local time.
In SimBrief you can vary the EOBT (Estimated Off-Block Time), but it needs to be entered in UTC/Zulu time.
Cheers
Ian