So about how much time is typical doing zone 4 (lactate threshold) effort on a "Zone 4" workout day?

Coggan writes that Zone 4 workouts are "typically performed in training as multiple 'repeats', 'modules', or 'blocks' of 10-30 min duration".

I did some Zone 4 climbing "blocks" today, governed by the terrain (Mt. Hamilton Road). "Block 1" was about 35 minutes, followed by a short descent. "Block 2" was about 20 minutes. Then I headed down, and the last return "block" was about 8 minutes. I felt fresh enough to do more, but I figured that 60 minutes of Zone 4 was adequate (and I'm watching out to avoid overtraining).

Garmin Connect says:

• Training effect aerobic: 4.3
• Training stress score (TSS): 161
• Intensity factor (IF): 0.914

Any recommendations? Am I being sensible, or just overly cautious?