To me it makes no difference.
Location is more important than time of day.
I also find the seasons to be better over others:
Autumn then Winter then Spring then Summer (best to worst)
Edit: the first 3 are pretty close but winter gets the gong narrowly over spring due to the start of the stormy season towards late spring/early summer. Love Autumn for detecting.
IMO a lot of people find different times better because they themselves are "operating" better at those particular times not so much that the time of day is the better detecting time over other times I.e. some people just aren't morning people, others get tired/distracted by the end of the day, detecting in the middle of the day in summer can be hard/not much fun etc.
I've heard a lot of detectorists say nighttime detecting is the best but I don't do any. I find it to be plausible though - nighttime a lot of things are quieter, conditions/emi can settle right down, less distraction/easier to get into the "zone". A bit more risky in some areas over others though.
I've done all my detecting between about 5am & 8pm. I couldn't pinpoint any particular time that I find better during those hours just that I have better starts, middles or finishes to days depending on a variety of factors - location (ground, wet/dry, new area - sometimes I have trouble building confidence in an area until I see some gold), how I'm feeling myself (tired, cold, hot, distracted), atmospherics & other EMI (powerlines - find some can cause more trouble at certain times, storms, signal towers).
I know some people believe that the heat of the ground can upset coils/detectors but I really think the above factors are more important & if the heat of the ground is enough to be upsetting your coil then you're not going to be real comfortable detecting in that yourself anyways.
