What duracellko said. Essentially you can stay in VATSIM and listen to others for as long as you like, assuming you won’t be blocking anyone in the apron or taking up precious ramp space in busy airports. Doing a radio check in the local frequencies is perfectly acceptable (even Unicom 122.8 could be used for that purpose if there are other pilots around but no ATC).
Or if you’re not interested in ground traffic, you could spawn at a rural airfield without a ground controller or other traffic, tune directly to the Center of that area and do a quick radio check or simply not say a word. Best to use an app like VAT-Spy before that though, so that you can tell which areas are manned by controllers at that time.
If you pick up a busy airspace such as northeast America (e.g. Boston Center 134.7) or central Europe, you’ll be amazed at the amount of work required by the controllers (so best to just listen and avoid radio checks there).