We've made contact with spirits in both.. but to try to 'prove it'.. or at least get some sort of evidence its best at night - when things are still and quiet. I did an investigation at the Edinburgh Vaults (Scotland,UK) during the day - but as it was underground it was just the same. Once we'd got the energies moving about a bit with some encouragement (music) - the invo was no different to being at night, even tho it was 10 in the morning.
I guess night investigations might make sense in heavily populated areas, but coming from a very small town in the middle of nowhere, I've always found it made more sense to investigate during the day. All the places I've investigated are pretty much just as quiet during the day as they are at night. I guess the best times to investigate vary depending on location.