Toller wrote:
Is there any reference on the internet about temperatures and durations that
are required to freeze pipes?

Every year I get neurotic when they start having frost advisories about my
cottage. I know it takes hours to freeze ice cubes at 0 degrees, so it
obviously takes more than a few hours at 30 degrees to freeze pipes; but
some actual data would be nice.

It is a big chore to shut off the water, and then I am without water until
next Spring.

First, any "reference" would have to be specific to some particular
configuration and so would be difficult at best to be generalized to a
specific location. I'd not expect to find much that would be directly
applicable.

In general, until it gets well below 20F for an extended period unless
a dwelling is completely unheated and there are openly exposed lines
the likelihood of a freeze hard enough to actual do damage is quite
low. The obvious is to have any exterior pipes like in a crawl space
at least insulated or heat-tape wrapped and have the space itself well
closed off to minimize drafts, etc. After that, remember that the hot
water supply pipes will freeze relatively more solid than the cold
lines owing to the tendency of the water heater to outgas the dissolved
oxygen. (Some say the hot water lines freeze "faster" than the cold,
but it's not so much how long it takes that's the problem but the lack
of expansion volume that causes the rupture in the hot water lines
before cold water lines.)

If one is going to be away for a significant time period it may not be
practical, but for short periods, one expedient is to simply leave a
couple of taps on those lines which are most exposed dripping so there
is expansion room--it's the lack of an expansion space for the volume
increase on the phase transition that is the cause of the real problem.
Obviously, for the entire winter this isn't practical.

Draining an entire system completely would be highly unlikely to be
necessary in any event--empty toilets so there aren't the valves to
freeze, obviously, open the taps so there isn't a closed system and
deal with the actual supply line that can't be drained or
pressure-relieved and you're good to go.

For the fall until actually closing the house, not knowing what the
place looks like or any more about how cold for how long it's hard to
speculate further, but I'd be quite surprised about having a problem
until it was well below freezing and remained that way for several days
unless it is bare pipe directly exposed.

BTW, shorter runs of smaller diameter tend to be more problematic than
longer runs as well as the hot water lines vis a vis the cold simply
because of the geometry between elbows is a shorter column for
expansion and the smaller lines have less latent heat capacity...