Good evening @Mf66,
I know a 4-5 minute delay is pretty significant. How long has this been happening for? Is the delay specific to certain numbers? How is the cell service in and around your location? Do you typically get 5 bars? How is the call quality?
I would recommend you to try and reset the Network settings. Just as an FYI, if you do reset the Network Settings you'll have to save your Wi-Fi info all over again.
Please keep us posted.