Gah! Stupid fat finger!
Anyway....
As for how long it takes... It's a bit like how long is a piece of string. Some women can go into labour after the first pessary. Others can have days of pessaries and the drip, but their cervix just won't dilate. And everything in between. Mine was ~31 hours start to finish. As I wasn't in labour until the drip, I was only contracting for 11 hours of that. Unfortunately people are much more apt to share the horror stories than the positive experiences, but I didn't find mine all that bad.
I don't have another labour to compare to, but I'm told it is much more painful on the drip. That's because there's no build up (other than the initial turning up of the drip). You start contracting quite hard immediately. But you don't need an epidural. Only you know your pain tolerance and what you can stand. I managed on gas & air and diamorphine, with some paracetamol + codeine in the early stages. But that's me.
Interventions are more likely yes, but it's partly because: baby getting a bit distressed due to the lack of build up of contraction strength, cervix not dilating (progressing) as quickly as they'd like (see: Friedman curve), and the likelihood of having an epidural. It's far from guaranteed you need one though. Other than putting on a foetal scalp electrode to monitor baby (the external monitoring kept falling off), I had no other interventions.
My induction was at 37 weeks. Had the gel pessaries, so couldn't go home. But then I wouldn't have been allowed to anyway due to the pre-eclampsia. The pessaries didn't do much. Couple of cramps, but certainly no labour. Once space opened up on the delivery suite, I had my waters broken. Still no labour, so onto the drip I went. After about 6 hours on the drip I needed more than gas & air, so had diamorphine. I was falling asleep between contractions afterwards! 5 hours later, once the morphine was wearing off, it was time to push. Ordinarily the drip would be turned down to let your body take over to push. In my case, my contractions started dying off and I had no urge to push. So the drip was turned up, and I was coached through pushing. 20 minutes later I was holding my baby daughter. A minor second degree tear was all the damage I sustained.
Good luck @grace1991. Hope it all goes well for you on Thursday.