In the summer ours are out all day (from about 5.30am) and in at night, but it the winter they go out in 2 groups in the old sand school (60 x 30) for about 4.5hrs each with lots of hay - they all seem really happy and content with this arrangement..............and no mud!!
I can have turn out all day every day if I want it, however my two cossetted ponies have made it quite clear that they love their stables and would rather be in when the weather is grim. they do go out every day but in horrid weather it might only be for 2 or 3 hours