A: With few exceptions, regardless of whether a watch has a wind indicator, the run times are designed-in the same, with the same requirements.
A watch stops when the power of the mainspring can no longer push through the friction of the mechanism, which is never zero. Exactly when this happens depends on many factors of the condition of the watch and the mainspring. The designers of the watch intended it to support fully winding and setting once a day, generally at the same time each day. And they intended that it still be running at that time. So "normal" is 24 hours plus some slack.
In my experience, the vast majority of usual and typical condition vintage watches run in the ballpark of 28-36 hours on a full wind.
As far as improving that...
The strength of the mainspring isn't the first thing to go after. If you think about it, all that's happening is the spring got turned X turns, it will "un-turn" X turns to move the hands. Power is slowly released by the escapement, but really it's just geometry; X turns in, X turns out. There
are no wasted turns. Even if a watch runs for 3 hours, no turns just disappear. It will just take that much fewer turns to wind it fully again.
In a perfect world. wasted power through friction would be close to zero. In this case the mainspring would need almost no strength to turn the mechanism. It's just about the number of turns. In practice, it really comes close to this. A fair condition watch, properly serviced, can be powered for well over 24 hours even by a nearly dead mainspring.
You can't gain more turns (and longer run time) unless you use a longer, thinner, and weaker spring, so that more turns can fit in the barrel.
A stronger mainspring, that turns the same about, may actually be problematic for an antique, that already has some wear on the mechanism. It will force the bearings to power through friction, more rubbing and grinding, on slightly damaged surfaces, causing more damage, where the watch would have otherwise stopped earlier.
A really unfortunate hack sometimes used in the old days by "botchmakers" was to get a watch to run by replacing a mainspring with a stronger one than intended - thus forcing it to tick. The replacement spring would be thicker, so fewer winds would fit in the barrel, so this was at the expense of run-time. Worse though, it was forcing the mechanism to run under more force than intended, potentially causing damage. Also, some original, actual, problem was left uncorrected. I've actually seen this in watches a few times.
But the short answer is that just because a watch has a wind indicator doesn't mean it's supposed to run that long. In fact, the wind indicator is one more little set of gears the thing has to power - more friction.
I usually set wind indicators so their hand is at zero when the watch is fully run down. In that way it likely does not fully wind up to its maximum reading. That way, the indicator truly shows run-time remaining as it was intended.
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