To setup discounts and surcharges, please refer to this article
To have a surcharge apply automatically:
Surcharges can be made to apply for a whole day.
In order to do this, you will need to select Maintenance then Discounts & Surcharges
1) Select the Surcharge
2) Press on Configure Auto Times
3) Select the day you want the surcharge to automatically apply on
4) To set the start time, click on the arrows to select the correct time in 24hr format
The start time should be set to begin before you open for trade
5) Press Set Start Time
6) To set the End time, click on the arrows to select the correct time in 24hr format
For the surcharge to apply all day, set time to 23:59
7) Press Set End Time
8) Press on Add Discount
9) The Surcharge should now display under Automatic Discount Times
10) Press Ok to complete setup.
Although it says Add Discount and Automatic Discount Times in the steps above, It will still apply as in surcharge setup.
Once a surcharge has been set to apply automatically, it will occur on every transaction and cannot be overwritten.