You can summon at any time. If you follow certain systems, you will find they might recommend summoning different spirits at different times, often based on the planetary association e.g., summon a Mars spirit in the hour of Mars etc. Some grimoires will recommend calling some spirits in daylight or only at night.
Usually we say, if you’re following that system, go ahead and do as the grimoire says, otherwise it doesn’t really matter. I summon anyone at any time and I’ve never had an issue, I think the whole timing thing is a more romantic approach, which can be great for building the psychodrama but I’m not that into the theatrics.
It is thought that 3am has a special feeling, hence the 3am club etc., but to be honest, it’s probably just because everyone else is likely asleep and the psychic background noise is the least at this time.
Sort of, if you consider seals or sigils or even enns/mantras/chants to work this way. It’s a fun analogy, but like any analogy, you can’t push it very far. They do not have 10 digit phone numbers with area codes, no. You CAN use your turned-off phone’s black screen as a scrying mirror though.
I don’t think we know, given that a grimoire that can work for one person can be a wipeout or another even at the best of times. You can try those that come recommended by other people, or avoid them based on negative reviews.
We know the medieval grimoires, and I believe including Crowley’s, come with deliberate “blinds” and obfuscations to prevent “the unworthy” from succeeding with them. basically you got told what those were after you were “initiated” by a teacher. There are some authors that reveal them in their own books… it’s a lot of hunting and reading, or figuring them out on your own.
That’s one of the attractions of modern grimoires written by people like EA, who have spoken out against such practices and said they don’t do this in their work, that all should be able to work magick and ascend not just those who pay for initiations.
What works for me is to not worry too much - I just pick one I feel drawn to, dive in and try it, like a cooking recipe, then edit and repeat adjusting to my preferences over time. I perform almost no rituals exact to the book, once you know how to cook you know your taste and what substitutions work and don’t work, after all. Don’t be afraid to experiment and have it fail, you learn either way.