I've been tracking internal and external temperatures for a greenhouse I've constructed. I would like to compare the rate of decline in interior temperature (at an hourly rate) comparing it to the rate of decline outside. I'm having trouble converting the time fields to calculate number of minutes elapsed between observations. Attached is a sample of the data showing date, hour of day, and observed tempterature settings. Your help would be appreciated with the conversion. I can get the hourly rate once that's figured out. Thanks!