Tee time range allows you as a club to set the start and end tee times that should be used for the calculations of the KPI's. Start and end time are set per month and if your club is closed during the year (e.g. during the winter) you can simply disable these months.
Why would I set them?
Some clubs might have their greens open at times that they do not see as a part of their normal golf tee times. This setting allows you as a club to filter out these results to give yourself a more accurate picture of your main golf tee times.
Do I lose the data outside of my Tee time range?
You will not lose any data if you narrow down your tee time range. Broadening your tee time range again will give you access to the data once again.