Time bundle distribution

I want to do some bundle distribution testing.
I want to activate a bundle to install on a number of machine and need to know on completion how long this took for each machine.
ie certain size bundle to 10 devices, 50 device, 100 devices etc
are there any log files that provide this info?
otherwise I want to set time variables at the start of the install and then again at the end to calculate how long it took.
Cant seem to get the variables working, any know ways of doing this or ideas...

Thanks