If you find customers bookings listed with 'None' in the stay time, this could be due to a few settings changes that may have happened; default table turn time, turning off table turn time or not having a table turn time listed in an override table turn time setting.
As you can see from below, the stay time box is saying 'None' and for these types of bookings, you will be unable to edit this.
To change this so you are able to edit the bookings stay time, you will need to ensure that the settings below are checked and updated as outlined below.
Default Table Turn Time
Ensure you have listed and saved a valid stay time in the 'default table turn time' here in minutes.
Disabled Table Turn Time
You may have disabled your table turn time here in the advance settings, 'table turn time'. If you have selected the tick check box for "If you don't want to turn tables at all at any time, tick here", you will need to untick this box.
Override Table Turn Time Edits
In the same advanced setting, 'table turn times' you may have entered in an edit and left the 'stay time' box empty, which will not allocate a stay time to any bookings made within that time period set for the edit.
In the example below, no stay time has been listed for bookings made every Monday between 8am - 9pm. You can delete this edit so you can then go in and edit the bookings stay times or you can change the edit to set a specific stay time.
When changing and edit, in the grey box where you specify the time period, you will need to select the check box for 'table required back by' in order to be able to input a stay time in minutes