I'm doing a brew tomorrow I think it's AG14 or 15 so not that many under my belt. The grain bill is quite small and I need it over and done with early, so I'm doing a 30 min mash /30 min boil for the first time. I usually allow 3l an hour boil off in the grainfather so I'll adjust my sparge by 1.5l to account for 50% reduction in boil time.
Assuming your klarstein boils off a similar amount, and it's just an assumption, then you'd be looking at 4.5l boil off in 90 minutes, so 3l in an hour, therefore reduce your sparge by 1.5l to account for 30 mins less boil time.
In your case I'd disregard the reduction in mash time quite happily, any difference will be so subtle as not to notice in reality. Hop utilisation reducing from 90 to 60 mins should be minimal also, and not have a noticeable effect, unless your a professional tea taster or something, so I'd not worry over that either. It might affect colour slightly but I doubt that's a consideration for you.
What you should do though is measure your preboil volume and post boil volume accurately, so next time you'll know exactly what your boil off volume per hour is for future brews. Also you can always dilute your wort back a little if you boiled off more than expected and ended up with a higher than planned OG.