Are you changing with data in-place or just blank? If it's blank, it can still be quick. If you are using a conversion tool with data in-place, and you have a full TB of data, it could take a few hours. Assume a nice, round 100 MB/sec. 1 TB is (on disk drives) 10,000 times 100 MB. Twice that for read and write, and I get - half an hour. I must be wrong in some assumption. Sorry, I can't help you there.
But if you are going to convert existing data from fat32 to NTFS, please make a backup copy somewhere else just in case something goes wrong with the conversion. It's unlikely, but possible.
If you are converting an empty drive, it will still be a couple of minutes.