This is a good question, it varies between my tables a lot.
D&D 5e (online/DM): Zoom opens at 7pm. A few minutes after everyone is there (we need some time for hellos) I will either launch into a recap, or set the scene evocatively (including senses not sight) and then we get into it.
Masks: A New Generation (in-person/GM): Plays occasionally weekend day, a lot longer time frame then the other games which happen after work. Also it's for my kids, niece & nephew. Usually plan on 45-60 minutes after we get together of catch up and socialization, at which point someone will go "D&D?", a running joke from the 5e game I ran for them, and within 5 minutes they are settled and ready to play. Usually either starts with recap and setting the scene if we're picking up directly from last session, or an "In the News" if time has passed.
D&D 5e (online/player): Chat opens at 6:30pm, game starts at 7:00am. DM announces start and we go. Cleanest cut-over.
Call of Cthulhu 7e (online/player): Game is supposed to start at 8pm, but really that's when we all get online and end up chatting waiting for whomever is latest. And then for like 10-15 minutes later. During this we are handling any bookkeeping, such as if we get to make skill advancement rolls. Transition to play is sometimes a bit awkward - we all like to chat and often the first call to start gets delayed by "one more thing".