Time above Zone 2 during base building

How long is too long to be above Zone 2 while doing base building to get the maximum benefit from the base building training? For example, if I go for a 1-hour run and my heart rate jumps over my Zone 2 range a number of times but I bring it back down, and I notice at the end that my HRM says I was above Zone 2 for 10 minutes altogether, was that too much time?

Thanks,
Mike