For the evisa application where it asks for intended date of arrival and flight number, I don't have a return flight to thailand booked yet and will book one after it gets approved, what did people put in this box? Especially for flight number?

Hi. I am applying for the DTV under the soft power provision. On the application in the travel information sections n it asks for the intended date of arrival and the intended date if departure. For the intended date of departure do I need to put 180 days since the stay is renewed every 180 days OR do I put the 5 years? Thank you in advance for any insight you may offer.