AS2::Removing text from a string

I have a time format like so: 00:00:00.00 (hours, minutes, seconds, millieseconds). This is stored into a string called adminTime.

But I need to make it so that the string takes what ever the time is and changes it to 00:00 (hours and minutes)

So basically a way of looping though the string and removing the seonds and milleseconds.

Thanks for any help.