It looks like teams start off from mid-afternoon to evening.
Linear leg?
What I don't understand is, how is bright when Kelsey & Joey are at the U-Turn point?
Detour - Logan & Chris spotted at night (unless that's not a Detour??)
U-Turn - Kelsey & Joey spotted here while it's bright
Roadblock - Tiffany & Krista spotted evening ish
In the season preview, there are shots of Justin & Diana and Tiffany & Krista running with children. I can't tell if it's bright or dark-ish in the pictures, but it seems like the latter.