Daylight vs. Nightfall ~ a possible new trait idea?

[Kristal]

You don't have to sacrifice anything in order to utilize it.

You'd have to gear PLD to cover the missing Regen during the 8/24 hours of nighttime, and DRK for the missing Refresh 16/24 daytime... so you're sacrificing either way... (Fringe logic ftw)

WHM has Auto-Regen because they cast so many cure spells they got 'poisoned' with the stuff. SMN has Auto-Refresh because they summon so much their bodies are partially in the astral plane. (Which also makes them sterile, which is the reason it's called forbidden magic...)
PLD has Auto-Refresh because RDMs have cast the spell on them so much they got sick of it and made a pact with a demon to maintain a global Refresh spell on all PLDs. (Unfortunately, pacts with demons rarely end well for the pactmaker, and the demon gave all other RDM spells to every other job as well...)

[MDenham]

WHM has Auto-Regen because they cast so many cure spells they got 'poisoned' with the stuff.

wat

In conclusion: 8 hours a day of 20hp/tick Regen, 8 hours a day of 5mp/tick Refresh, 8 hours a day of 250TP/tic Regain.