My Time Dining only applies to the Main Dining Room. The Windjammer is open seating for all meals and is a "buffet" type option and the there is no real dress code in the Windjammer. You do need shoes, shirts and cover ups over swimsuits.
If you do select My Time Dining you will need to pre-pay your gratuities.
I know you will enjoy all the Freedom of the Seas has to offer and enjoy the cruise. It is a large ship and you will not be bored.