Policy is the same 7 days before or 30 days after, it is also written at the website on booking page where the options are offered. I got today morning also email about schedule change, it was slightly less than one hour for the lh segment. Since I do want to change two segments instead of one to later date, it is not possible through the website. IST-Europe segment is not upgraded with voucher due to the lenght of IST layover but now when trying to change the date, it goes to J and TK asks 4 digit euros to pay just for IST-Europe upgrade .
Sent the chosed flights to TK contact, will be done on the next week since today is Friday. Recommendation is to contact local office and wait, it takes time and the weekend is coming.