I've been messing with the days and time in minecraft to see the seasons in action... nothing seems to be occurring, I'm wondering if it could be a mod like dynamic surroundings or better foliage getting in the way?

Edit: Been playing with the season clock and I'm adding days 1 by one and I'm not noticing the season clock moving at all.
Edit2: Tested with only tough as nails mod loaded, seasons still aren't changing :(

... I take it no one else is having this problem?

Do the seasons not change based on days? Because I think I noticed a change, but from regularly playing and not from /time add

/time add is not intended to progress seasons, /tan setseason is. Sounds like this is just a mixup in commands

Thank You! I couldn't find any info on the TaN commands :)

Did you have a look at the wiki? They are documented pretty well there: https://github.com/Glitchfiend/ToughAsNails/wiki/Commands

... I had no idea, so many times when I click on a github wiki it just shows a blank page, guess I got used to it :P