How long before the fun starts?

If you mean how long until penetration, My Mileage Varies Wildly.  But fun?  At once

I have had some licking my tonsils and taking off my clothes as soon as the door closes, and others easing into it with some conversation. If we are not both naked within 15 minutes though, somethings wrong, and things better start hsppening really quickly.  (unless it's a multi hour date.)

I have a tendency to get things going right away, after you've washed your hands/showered/etc. I save the talk for afterwards, because I've found when you talk first that sometimes you aren't able to get everything done by an hour. I'd much rather be "in action" for the first 50 minutes and then talk for 10 than to talk for 20 minutes and not be able to complete the deed! Though, I've never been a clock watcher type anyways, and often go over the set duration, but that's how I like to do things. I don't like to rush, ever. I like to enjoy myself as well as make sure you enjoy yourself.

usually within the first 5 minutes, sometimes a little longer.
Today I met with a lady I'd seen before, and we were DFK 5 seconds after I walked in the room.

With the lady I have seen the most, it is usually within 5 minutes, but with some others it has been as long as 10 minutes as we got thru preliminaries. I usually do 2 hours at least, though.

the moment I walk through the door.  I assume it is an unscientific way of getting a feel for whether I am LE

but with repeats, the initial hug & grop is about the time the latch clicks on the hallway.

That's when.

If she's good, she can tell.  If she misses the cues, ask if you can give her a kiss, then begin.