When reading a manga, can you tell if it's night or day?

Sometimes.

Yeah, this is why establishing perspective angles like lampposts etc., are often important. :P

A lot of times context will tell you as well. If a scene shows a class being taught at school, or it's at school between classes, at lunch or during club times, it's obviously during the day. Same for walking to/from school. It can get iffy in some situations, like people at work, but often there's clues that'll help you. Does the protagonist work for a black company? Then scenes will often be at night to drive home that they're being abused by their employer. If they don't, it's probably daytime most work scenes.

Laura is back ! Heya

Oh, you talk with her?

Her?

Nope !

Oh, oke.

You rarely chat with other girls around here. I think the only one we chatted regularly is Ms. Blue.

I come and go, sometimes I don't feel like accessing Gelbooru for months at a time, or I'm accessing it but don't feel like commenting any. I try to put thought into what I say and sometimes I'm just too tired or too busy to bother. Or I may be more interested in using my energies to work on tagging or translating stuff instead. There's also periods where I don't see any images I really feel like commenting on as well. I can be quite picky about the stuff I like.