Unless Nitrogen is not going to issue you the segwit2x coins, there is really no point in withdrawing. Just to inform you, even exchanges disable withdrawal and deposit of bitcoins 24hrs (or even 48hrs) before a fork happens. It's a normal procedure for them to be able to access how much of the altcoin they are going to give out to each user. I do think it is fairly reasonable to do so as it prevents the possibility of over sending the newly created coin.

I am not sure though if Nitrogen is going to give out the fork coin after the fork, so check with them.