i had the same questions when starting vit d supplements and i found these aspects:
better take vit d during the daylight hrs because your skin is supposed to make it by sunlight so the body may have a better way to work on the supplements if you take them during the day
i also read somewhere absorption and use of vit d is improved during daylight while taken at night it may disturb sleep
the difference from sunlight made vit d and supplements is that sunlight vit d is produced slowly so i usually take 5000iu at breakfast and 5000iu at lunch
if it is vit d in dry form you need a fat meal to absorb the pill, if t is vit d in oil liquid or pills with oil liquid no problem.i m using dry pills lately so i take them at meals together with heptech PPC which improves absorption