...you paint them? It's been about a day since I painted it.

If the paint is dry to touch - you can put them up. If it's still a bit sticky, wait a little bit more.

Wait til the wall is dry...if your using tape, id wait for a week after the paint is dry so it has time to cure and the tape wont peel the paint off the wall...if your using nails or tumbtacks...put it em up when the wall is dry

It really depends on the type of paint you used to paint your walls.

Here are real answers:

If you used acrylic (latex) based paint it will be dry to the touch within two hours if you used one coat, three hours if a second coat was applied. This is assuming that you're keeping your house cooled at normal temperatures between 70 to 80 degrees and the humidity is in the normal to low range. Add one hour to the waiting time for latex paint if you used semi-gloss instead of flat.

If you used oil based wall paint you do have to wait 24 hours. Add four more hours to that if you used semi-gloss oil based paint instead of flat. And here again, this 'cure' time is with the assumption that you're maintaining a temperature range between 70 to 80 degrees and the humidity is also in the normal or below normal range.

You can deduct from the cure time if the house or apartment has been vacate and the A/C turned off. The hotter the temperature the faster the drying time.