Please provide your PNR of the ticket you already booked.
About return ticket Tatkal opens 2 days before at 8 a.m. but it depends on from where the train starts. e.g. if trains starts from delhi on 6th then tatkal will open on 4th. if it reaches station in between on next day and the station is having tatkal quota then it can be booked on 5th as train comes at that station on 7th. I hope i am able to make things clear to you. But safe is to book from the station from where it starts and get the boarding changed from near by station.