If a race has time limits they should state them on their entry forms/event info, so if they don't you should be fine.
Tumble turns generally not allowed due to safety issues (there will be several of you in each lane) so there's no problem there. Protocol is if you want to overtake someone, just touch their feet and they let you past at the next turn.
They will generally ask for a time estimate for the swim, and put people in appropriate groups based on that, so you should be swimming with people at similar level. If it is your weakest event, you can have just have more fun passing people on the bike and run!