the humidity in the tent is between 60 and 70%, even though I don't have a humidifier. I don't know why. Should I lower it or how can I lower it?

60–70% RH isn’t too bad for veg, but for week 8 autos that should be flowering, it’s a bit on the high side that could slow them down or even delay bloom under stressy VPD conditions. Try improving airflow (extra fan or open vent), and if possible, place a small dehumidifier or a bowl of rock salt in the tent. Keep temps around 24–25 °C lights on and you should see them respond soon

Plants 'transpire' through the leaves. The larger the plant, the more moisture it will pump into the atmosphere. You can extract air to an area where it can't cycle back into tent's room, or you can buy a dehum. The first requires ambient RH to be equal or lower than your tent's target RH and if that is not the case, extracting won't do shit but move air that has too much moisture from one area to another... not effective. You can also choose to grow during seasons with low RH and possibly avoid needing a dehum. Dehums also add heat. It's much cheaper to add moisture than to take it out of the air. If it is 8 weeks above ground, good chance your 'autoflowers' are actually photoperiods. This happens from mispackaging or pollen contamination. It should not happen often. If it happens repeatedly, stop buying from that source. Expect them to at least double in size. If this is too much, prune them back and give 12hours of light / 12 hours of darkness. May want to prune and let it heal for ~5 days before flipping to a photoperiod flower schedule. If you go to 12/12, stick to it. You need 150% more light to maintain same dli over 12 hours vs 18 hours, otherwise you are just providing 2/3rds the dli.

Autos will bloom when they want some autos are fast and small and others can get huge