@MeneerJacco you might check this entry as well, which points to a small web page doing the calculation work reg. at+cpsms command.
https://forum.iotcreators.com/topic/642/psm-calculation-tool-t3412-t3324-value-decoding?_=1622307153602

Be aware, that entering the value via at+cpsms is only a request towards the network. The network decides if your values are committed. To check the network reply, use

at+cereg=4

and check the values via:

at+cereg?

You can paste the reply in the above mentioned web page as well to get the values ‘decoded’.
My recommendation: set the active time (T3324) to a minimum and use the ‘RAI’ - release assistance indicator after sending data to shorten the RRC connected mode to a minimum. Then your device will enter PSM faster.
BR,
Markus

Which power saving features are covered by NB-IoT over classical LTE?