Holds are easy to do.
Force a key on all the relevant bones at the start of the hold, then copy and paste those keys at the time where the hold would end.
If the keys are zero sloped the hold will be absolutely still, which you probably wouldn't want in finished animation.
To make a "moving hold" you typically adjust some of the keys at the start of the hold so that they haven't quite reached their destination and instead nudge into it over the time of the hold.
Good moving holds are tricky to do, and if you are still in the blocking stage it's pragmatic to leave them non-moving until you've ascertained you like all your acting choices and are ready to polish.