Mine approach depends on the column, and is usually for about an hour.
For thermally-resistant non-polar columns, I usually bake at 20C above the method's final temperature, or 20C below the isothermal Max, whichever is lower. For polar columns, I usually bake at the method's final temperature.
I would only increase the baking temperature if peaks were still coming off after an hour or so.
My experience is that, with good quality columns and carrier gases, high-temperature operation of non-polar eventually results in column rejection because of brittleness, rather than performance. For polar columns, they tend to croak if they see oxygen or muck at elevated temperatures, so I tend to minimise thermal exposure.
Please keep having fun,
Bruce Hamilton
