Only just started this week but at the moment I'd say 35 minutes max in the morning: turn out (no rug), muck out (straw bed, hopefully fresh straw in every other day), fresh water and empty haynet into corner of stable. Then quick change in the feed room! Reckon it'll go down to less than half an hour when I get into the swing of things.
Thats 2 horses that are in over night, sleep in their turnouts to save time, have a deep littered straw bed down. Takes me 10 mins to turn out, then I skip out add fresh straw, scrub water/feed buckets, fill water buckets, soak feed for evening, empty barrow, add barrow of haylage to each stable, sweep up, rinse my boots off, get in car, go to work.
I spend between 45 mins and 2 hours down there at night.
When she's in at night, I always consider if anything happened which meant I couldn't bring her in myself, so I try really hard to do everything in the morning (not that I always succeed!).
So, I muck out and change rugs while she's having breakfast - tied up outside if it's not wet - chuck her out, then fill her haybag and water bucket. If she's been too wet in the night I'll put the bed up to let the floor dry out, otherwise I'll just leave it down.