Hello people!

Its many years ago that i programmed something. Now i need to calculate the average speed of a car after pressing a button for start. I programmed a distance counter with a PIC16F88 and need now to measure the real time and divide distance by time. In my opinion that needs two interrupts.
The distance is measures using "on interrupt" counting pulses from the driveshaft. Do I need two pics or one pic and an external clock?
I could only use two types: 16F88 and 18F1320 becauce I´m an inept programmer.
regards in advance for any helpful suggestions.