the best part about a lap endurance race is you cant "not finish", as long as you do one lap you finished. the hardest part about lap event races is that you know you can be done and not have to go back out to ride again. this is mental mind-F for me. do another lap to not gain a place or pack up 30 minutes early and hang out. if its a big loop, you have no choice to but to ride it out.
4 hours is just long enough that you can push the limits of XC pace for the normal race time, say 90m to 2 hours and whatever happens after that, happens. even if you just JRA the remaining laps, you may either become a zombie, or find the zombies. you'll learn. DO IT!
Yes and no on the no DNF- it's possible that this is not always true. Many races have a rule that says if you cross the finish line before time is up, you
have to go back out for another lap or else you'll DNF. The obvious solution is to just hang out and wait to cross the line until time expires, but if you don't know that, you can accidentally get yourself a DNF. Iron Hill used to be like that - I'm not sure if it still is. But it always cracked me up when I'd come through the start/finish are at like 3:40 for the 4 hour race and I'd see half a dozen guys just hanging out with their bikes 20 yards from the line.
Some other races flip the rule and say that you have to finish your last lap before time expires. This won't necessarily lead to a DNF, but you could end up riding a whole extra lap that doesn't even count. Personally, I love this format because it forces you to think about a lot of things as time ticks down -- how fast do you have to go to finish that last lap in time? Can you even afford to stop at your pit? And, of course, will it even matter if you kill yourself to finish one more lap if you can't catch the guy in front of you anyway? Races like these are rare in this region, though - most go by the "start your last lap before time expires", but I've done a few races in the midwest and down south that seem to use this format more often.
As far as whether or not you do it,
@Jeffreywoliver , I say go for it. Endurance races are a lot of fun. If you're new to them, you should really feel no pressure. It's just like cat'ing up in XC: the first few races you do in new categories are always just to gather data and learn. Find out if you enjoy it and put zero pressure on yourself to finish at the top of the standings. If you do finish high, that's a bonus. If not, you have a built in reason - no matter how strong a rider you are in general, this shit is all new! See what works for you in terms of nutrition, pacing, rest, etc. Lap races are great intros because you can stop at your pit if you need a break. Once you know how long you can ride without needing that rest, then you can probably start thinking about more single-loop endurance races like the 100 milers or 50 milers or whatever (if you want to try those - no rule says you have to!)
Oh - and one thing to be aware of that really shouldn't ever scare you off:
every race you do, whether it's 5 miles or 500 miles, will
always go off the start line like everyone is racing for five minutes only. But in endurance races, that will also
always slow down pretty soon. The sharp end of the field will hold a pretty brutal pace for a while, but even they're going to settle in to a pace ride at some point. For most endurance racers, the goal is separation. Get yourself out of sight and pretty soon you'll be out of mind. That's why those guys go so hard early - they just want to get themselves away so they don't have to fight all day. For the majority of racers, it's really easy to get caught up and intimidated by the pace early. Don't be. No one can hold an XC pace for the duration. The best thing you can do is figure out how to manage the craziness early and slow yourself down when you need to, not when everyone else does. Believe me, half the guys who ride away from you at a crazy pace early you will see again if you're smart. Because a lot of those guys won't be smart. A lot of the guys who look really fast and strong won't be able to hold that the full day and they'll blow themselves out because they don't know that. A few will stay away - there are always guys who are just plain strong. But it's not as many as it will appear to be early.
Give it a shot and good luck to you! Hope you enjoy it!