Bitcoin rallies over $18k... time to sell?

Depends on your timeframe. If you're trading short term then maybe now is the time to sell. If you're in it for the medium term (3 months - 2 years) then selling now would probably be a terrible idea. If you want to learn more, I recommend the following youtube playlist, click the bitcoin one once on Youtube.

https://www.youtube.com/c/ConquerTrading/playlists
 
I am a little bit ambivalent on this. I agree with @bpinon that if you trade on a short timeframe it might be the time to sell, but - while I doubt this is THE time to sell, as it is still predicted to go higher - I don't necessarily think it's a horrible idea to sell even if you trade with a longer timeframe.