After checking internally, even we have no specific travel dates field in Inventory tool, you can load an Early booking offer with specific booking dates following these steps:
Create a derived rate in Set up tool with the specific Booking dates you have for this Early Booking offer
Load rates in this derived rate using our Manual Load option, only for the check-in dates the booking is applicable for.
Make a quick availability check by using our Availability tool
We will keep gathering interest in order to add travel dates into available loading fields in Inventory app and keep you posted about it!