I try to keep out of the ditch whichever tire I'm running... oh.I see the second question now: when to remount regular tires. (Sorry, must have forgotten the medication!

)
I suppose if you like swapping tires back and forth, you could do it every warm spell/cold snap. While snow is possible here in April, Mid March usually sees the last of the storms worthy of studs and deeper tread. So the Ides of March are not quite as bad for my studded tires as they were for Ceasar, as I don't usually take a knife to them, so maybe that's why I've never heard them say "Et tu, Brianus".
I can believe its April for changeover in Calgary! Wonder when in Alaska?