Inconsistent workout tracking

Doing all you suggest but still having erratic readings. They are off as much as 7 minutes and as close as 1 minute. I understand the 1 minute as it cannot be that accurate. However, I just finished a 39 minute walk, at 3 mph or more, arms active and watch secure (not tight and not loose). I do notice that my early morning walks in cooler temps seem to be more off than later afternoon walks when weather is much better. Does the outside temp have any impact on heart rate? Can't have any impact on motion.

Not happy about the inconsistency..