i wodnder if it is safe to withdraw BTC now from Waves DEX, with all that at the end of the month, will it take longer or something or better not moving the BTC from where it is? (on the DEX) 
From what I understand it may take a little bit longer than usual right now, but not hugely longer. I think they are making you wait for 6 confirmations for the time being until the Segwit drama fully resolves itself. You can certainly leave it on the Waves Dex until after everything settles down. I don't think we've been given definitive word as to whether the Waves team might be capturing and sharing BCC (Bitcoin Cash) for BTC held as WBTC on the Dex. If your motivation is to make sure you receive BCC then you're safest to move your BTC to a private wallet you control.