First off, we know Dracula returns ever 100 years. More or less. So, how long does he actually stay? Some games it feels like Dracula shows back up on a Thursday and he's laid back down by the weekend. Other times, it feels like he's got a good portion of the countryside terrorized before anybody even starts to go after the guy. Castlevania 3 comes to mind there. It really felt like his terror had a chance to spread.
I think there is no precise way to tell how long does he stay. In every game, the time for him to stay on Earth seems to be drastically different, as you have mentioned.
He stays for as long as there is no hunter on his doorstep, I guess.
Likewise, can you tell when Dracula is about to resurrect? is there aq slow increase of spooks and specters and general creepiness around the area, or is just suddenly, "Drac's back!"
The general rule is "Dracula returns when the faith of men weakens". On the Castlevania universe, if shit's going down big time somewhere on Europe, you can bet Dracula is creeping around the corner. Still, plenty of times the populace growing lax (Castlevania I) or one dude holding too much power and getting corrupted (Barlowe) is enough to bring Dracula back into the game.
Simon's Quest does imply that the increase of evil creatures roaming the land and gathering in some region is an omen of Dracula's eventual return, and the CoD manga says that the animals feel the flow of darkness and start gathering where it is stronger. So I guess this can also be used as a compass. See sudden increase of ominous animals roaming the area? Beware, Ol' Drac is near.
We see castle crumble in most of the endings. How does it come back? Does it rebuild itself over time. Do the villagers just look one day and there's a huge freakin' castle where there didn't used to be a castle? Does it shoot out of the ground fully formed like a bat out of hell?
Curse of Darkness shows the castle returning from inside a lake, outright rising fully formed, bridges towers and all in less than 15 seconds. It also shows that it's a pretty violent occurrence, with the lake getting very violent and the land shanking before the castle is settled. This conforms with how Belmont's Revenge shows the castle's return: same thing, just as fast with land shaking and violent lake stuff.
However there are also instances of the castle appearing on land (e.g. Portrait of Ruin). Order of Ecclesia shows the castle suddenly already there. SotN says that the castle "appeared out of the mist".
So my conclusion is that the castle does indeed appear in a quick instant: One moment there is nothing, one or two minutes later it's there as if it has always been there.