Thanks, how long it will take them before new nodes start giving rewards? If longer than 10 days, does it makes sense to unstake and switch to another validator with better rewards?

It might take way longer than 10 days, but if you were happy with them until now, i would say to stick with them also in the "hard" times.. it might be worth it after the 3 nodes become active :)

No, it doesn't - rewards average out over the year, jumping providers is not worth it; however the drop to 8% if advertised as such doesn't seem right to me, if you calculated that you only got 8% and it shows 12% that makes sense, rewards will vary based on active nodes as Emil said.