it was no problem when I arrived here from Kanchanaburi. TM30 filed by landlord then a week later did the 90 day online with Krabi, a week before the due date.
If you have the 60 day tourist visa, your carrying airline will want to see a ticket out of Thailand within 60 days, as per the rules of the visa application.
This doesn't have to be a return ticket, but only out of thailand. A fully refundable one to some where cheap, out of thailand, is good. You can then cancel and get refunded after arrival in Thailand. extend your visa 30 days.
Avoids the crazy fees charged to move your return flight leg 30 days.