Problem
When I generate my bill the time entry for a previous day is appearing as the date of the bill.
Solution
This may be because the parameters in your system have been set so that where the activity code for that time entry is used, the costs are summarised on the bill.
This means that when a bill is generated with that activity code, all of the costs that use this code are aggregated and given the date of the bill (and the generic narrative of that activity code).
If you would like this to show itemised on the bills and to have the date the time entry was entered, you will need to go to Parameters > set Parameters > type in the activity code letters, "AC" then find the relevant time code, right click and modify.
Untick the box that says "summarise on bill". Go to File > reset login settings to apply the changes.
Updated