Most women don't notice any significant change in their temperature during a one-hour time change. If you're one of these women, or if you're not in the midst of your fertile days, ignore the time change and take your temperature at the usual hour. For example, if you take your temperature every day at 7 am, continue to take it at 7 am after the time change. In these cases, one slightly higher or lower temperature won't affect your chart interpretation.

However, if you notice a significant change in your temperature in the span of that one hour, or if your ovulation is impending, you may try to gradually change the time of measurement. Start to take your temperature half an hour earlier or later on the day before the time change. For example, if you usually take your BBT at 7 am, and you know that on Sunday the clock will be moved forward one hour, you should start taking your BBT half an hour later on Saturday (at 7.30 am) and another half hour later on Sunday (at 8 am of the old time, or 7 am of the new time).