You can run it right up to PCT, but at that point, I would cut it out. Once you go into PCT, you'll want to be careful with how low your cals are and creating any more of a deficit you create with fat burners.
As for keto, I don't use it and I still get fat burning effect from clen. It may not be quite as strong after awhile, but it is still going to work. It won't hurt to throw it in, in the 2nd half of your clen use though.
Also, I would make sure to tapper off of the t3 for a couple of weeks when you are going to discontinue using it