When working with Excel documents (or any other files) you should be protected from losing all the work in case of power loss, computer crash or other unspecified reasons, which may ends that you have to start all over again. To check whether your Excel AutoRecover feature is enabled, you should go to Options in the main menu , find the Save section on the left hand side and make sure the option AutoRecover is selected.
You are free to modify the AutoRecover time to set the time interval that suit you the best, but remember, when the AutoRecover is executed, Excel Workbook will blocked for some time. The time necessary to save the AutoRecover information is related to the file size you are working on, so on bigger files Excel needs greater time to save.
If you set a short interval between two consecutive AutoRecover actions and you work on the large file, you may find that working with the workbook is at least difficult.