In the prelude to Glorious Revolution, Protestant dissenters collaborated with William, cousin of James II, to hand over the throne to Will (who is Protestant and therefore more tolerable). In OTL, William was a little bit worried about the English Navy (which was mostly loyal to James at that time, unlike the Army which was divided in loyalties) but took the plunge once his English conspirators talked him into it.
Suppose that the conspirators get impatient and raise a rebellion before convincing William to come over, thinking that capturing London or James II will give them a quick victory and they just need to roll out the carpet. Based on estimates of forces at that time, most of the army is not mobilized. Assuming men stay loyal to their officers, the rebels can quickly put London under siege with about 9K vs 3K within a week, but have no heavy guns to bombard since most of the land artillery is in the concentration of seven armories, all far from London. At march on contact (where troops try to reconnaissance for enemy flanking instead of marching as fast as you can without getting tired the next day), it would take considerable time for either side to mobilize a unit that isn't ready and march it to London.
I have three questions. Answer the third one if nothing else please.
First, can the rebels simply overrun London if the enlisted men of either side stay loyal to their officers in the opening stages?
Second, what is the most likely development if William waits instead of going to England?
Third, is it possible for William to wait and do an "option play" plausibly? What I mean is that do nothing actively, but be in good face of the winner? Like if the Whigs/rebels win, come over and be on their good side with the excuse of something like "well, you know an invasion is a logistical work and you guys started before I was ready, so I could only send money not troops" (an amphibious invasion is indeed a lot of work by the way, especially if it is opposed on landing) and if the Tories/loyalists win be able to say to James "I know we have our religious differences, but we are family and I'd never betray you. Some of the people in my household have been acting on my behalf thinking they know what's best, but I didn't want them to undermine you."
In other words, if the dissenters turn into rebels prematurely, can William retain plausible deniability with waiting?