Well it's a personal thing - i like to set laps based on how i feel. Could be after 5k or 10k in a 70.3 race.
So manual laps would be best.
So I tested hotkeys for lapping in a multi-sports activity and there's good news and bad news.
Good news: they work
Bad News: 'Lap' actually is 'Back' and goes to the next activity :-(
Not sure if this is a bug or not, I'm going to log it and see if Garmin have anything to say about it.
CW