It's not as much an issue of pressurization. It's just that the 744 will not descend in VNAV while in CLB mode. To get it out of CLB mode, your options are (1) install an approach for a return and have the first fix of the approach in 1L, (2) re-cruise (insert your present altitude on either the CLB or CRZ page and altitude intervene), or (3), according to CCA, select DES now, presuming you've already installed an approach at your destination airport (we normally do this prior to departure).
Installing an approach for a return should not only reschedule your pressurization, it should make moot options 2 and 3 for getting out of CLB. But there are times when you would want to descend and perhaps dump fuel in a hold for 40 minutes and you don't know what approach you would be using at that point. As Mustafgander pointed out, you could simply use FLCH or V/S to do the descent, but I was curious if DES NOW would get it out of CLB mode so you could descend in VNAV.