Date and time for a new LAST position

[routeconverter]

The LAST new position, however, used the time I added the position, instead of keeping the correct date. I know it had nothing after that position to use to calculate the correct time

That is the reason why "keeping the correct date" is impossible. No date is another alternative.

but better than what has happened would be to use the prior two date and time values to calculate the date and time based on keeping the same speed as an assumption of the speed of travel in calculating the correct date and approximate time to use for this new position.

Let me see how complex this might become...