These commands work fine: (calculates time between opening and closing the program)
time gedit time emacs time vim
But this command always gives a time under 1 second. It's probably time which opening the program took.
The GUI version of vim will detach from the foreground terminal by default - you can tell it not to - and so has "exited" from the point of view of the time command.
Detaching means it doesn't block the terminal which, for a GUI application, is a pretty reasonable choice.
Your analysis - that this is roughly the startup time - is on the money.