Drawbacks to getting dressed at 5:30 a.m.:

1) if your clothes don't fit very well, you are much less likely to notice at that hour due to your sleepiness and/or the poor lighting and/or rushing (or in some cases, all three).
2) The weather at 5:30 a.m. is hardly a reliable indicator of conditions later in the day, so you have only a 20% chance of wearing appropriate clothing, even if it does fit.

Example: Today I'm wearing a pair of pants that really don't fit very well, and a sweater that's way too warm.