Will I still be able to do this many months down the line?
Or is time a factor?
If you have the private key, there is no time limit (as long as nobody else gains access to your private key).
So All I need to do is use my BTC address the funds were sent to (device no longer have PW's for) and I can return the funds to the BTC address I sent them from?
No. Bitcoin wouldn't exist if that would work. You need the private key for the address that currently holds the coins.