I heard it takes anywhere from 2-3 weeks, but I was able to log into nucleus with the User ID they give you in the e-mail confirming your deposit.
If you get an e-mail with the title, like, "Welcome to PCOM! Deposit Confirmation: Biomedical Sciences - name User ID = ##########"
If you look at who else they send the e-mail to (other than your current e-mail), you'll see that they also went ahead and sent it to your new e-mail at PCOM! 😀
I e-mailed to ask how to login since there wasn't an option to create a password as a new user before logging in for the 1st time...so after you get the e-mail where you can figure out what your User ID & PCOM e-mail are, you click on nucleus from the PCOM homepage and log on by entering your new e-mail as the user and then the password will be only the last 8 digits of the User ID #.
Once you're in, you can set a new password!
Hope this helps! 🙂