I had to give Bracken sedation (Domosedan, sounds like a similar, if not the same thing) earlier in the year when the local hunt was meeting just down the road from us, as she gets absolutely hyper, sweats up and gallops about and won't calm down for ages after - she used to hunt and wants to join in again, poor girl!
I was told to give it about 45 - 60 minutes to work, and that was probably about right, she was out in her field, but away from the others, had her on a lead rope to start, and she wandered about nibbling grass, and then started drooping, and then planted her feet well apart when she could feel herself going wobbly, and eventually she just stood there with her head down.
Took the lead rope off and stayed with her, she did move slightly now and then, but nothing too much, and she stayed like that for about 3 hours at least, then gradually started to come round, although it actually took about 12 hours to properly come out of her system. as she was still a bit dopey in the evening.
She ate grass again as soon as she started coming round, I hadn't been told not to let het eat, and it didn't do her any harm.
Good luck with taking the staples out - do you have to do it yourself then, or does the vet come out to do it?