It just seems to me that with my low humidity, the
plants would probably lose more water during the day than they absorbed during
the morning watering. Would watering twice a day compensate for that, or not?
Any ideas?

I agree not to water twice a day. If you look at the leaves, they
are covered with a sort of waxy like substance. This helps prevent
water loss during the day, they do most of the metabolism at night in
another water conservation measure.
In nature, they get very little dew, and rain every day in summer
during growth season, but often once a week in winter when dormant.
They have adjusted to minimal watering, so no need for twice daily.
One of the main species in hybridizing, Tol. guianensis, comes from
arid areas with little rain and usual humidity of 30-50%.
I've got about 50-60 now in spike, and hoping the other 100-150 soon
catch up!! I'm in south florida, so I don't even have to water daily
when in growth, but mine get rain and 80-100% humidity during the
summer. These and leafless are my two favorite types!

jimwatts