We nearly always see frosts right up to our frost-free date
of May 15, but starting in mid-April, we also enjoy multiple-day
periods without freezing temperatures. It's worth taking the
seedlings outside for some of those warm days, especially as they get
bigger and more able to handle breezes and blazing sun.
Sunbathing-seedling afternoons also give me a chance to overwater pots
so water runs out the bottom without making a mess inside. This
type of watering helps prevent salt buildup in the growing zone of the
pots, and while it's probably not necessary with short-term potted
plants, flushing out the pots makes me happy.
If we lived in a normal,
climate-controlled dwelling, I'd have to be more careful of my first
stages of hardening off. But since our trailer often drops down
into the mid-forties at night at this time of year, similar
temperatures outside are no big deal for our seedlings. I do
continue to take them inside at night, though, if the forecast low is
below 45 --- our microclimate seldom matches the forecast, and it would
be a shame to lose all of these little tomatoes and peppers to a freak
frost.