wrote:
Can I get recomendations for the most accurate electronic timer that I
can buy?

It must to be accurate to within 1/60th of a second over the course of
6 hours.

Is something like this commercially available, or will I have to build
it, or have someone build it?

You will certainly find what you need here, though whether it is within
your budget may be another matter. They have units that are far better
than 1ppm accurate. http://www.symmttm.com/

Or, have you considered a simple PC application that syncs its time from
NIST via the Internet using an NTP client? Virtually free and accurate
to 10ms, as long as you can tolerate a net-connected PC.

Or, perhaps a PC / system connected to a GPS receiver via the serial
port (though I understand the time via the serial port may only have
1-second resolution for many units, so homework is in order).

Richard