You can record 1,000 folders and each folder can record up to 100 individual transmissions. You're pretty much wasting your money if you buy an SD card any larger than about 8 GB because you just can't get any more audio on the SD card in most cases. I've been recording a lot of the protest and riot traffic in my area and I had to take the audio recordings off of my SD card after 4 weeks there was so much traffic. I've never had it fill up that quick with 1,000 folders.
We used to be able to record more, but unfortunately there were some issues that were being caused and Uniden wasn't able to figure out what was causing the problem(s). So they put a limit of 1,000 folders on the SD card when it came to the audio recorded and that fixed their problems. It was causing some strange problems on my radio prior to the change they made. But I haven't had any problems since they made the change in late 2018 or early 2019. If you were just parked on one frequency recording fire or EMS traffic, and of course it depends on how busy the frequency is, you should be able to go for a really long time before you run into having to take the data off your card and transfer it to a computer.
It depends on the "balance" (or free space left) of your SD card. The size of the card minus files needed for the card to work, minus the files needed for the scanner to work, minus the space consumed by Favorites Lists. Each minute of recording takes up about 1 MB of SD card space.