You can insert more than one time window through the additional fields when importing routes. (Import routes details)
Your file must have different columns for each of the time window information. If, for example, your customer has two service windows, your file must have four columns:
Window Start 1
Window End 1
Window Start 2
Window End 2
When associating fields in your file with time window fields, you must associate two columns for each field requested. It would look like this: