Is the display strictly for output or is input also allowed?
If output only, then simply write to the display (with DFRWRT(*NO)), delay the program for 5 minutes, and then write to the display again. You can delay the program in a variety of ways: the sleep API documented here, receiving a message from a *DTAQ when the message will never be sent and using the QRCVDTAQ Wait time parameter documented here, using the CL DLYJOB command documented here, etc.
If you need to also accept input from the display then you can associate a *DTAQ with the *DSPF. The program could then be notified via the QRCVDTAQ API when either data is available from the device or 5 minutes has passed. This is discussed in Chapter 12 (Waiting for Input from a Display File, an ICF File, and a Data Queue) of this manual.
I hope this helps,