Start with 10 days. Go longer if you feel you need to nearing the end of the cleanse.
I do get sick of the lemonade. I like lemon water. And I like maple syrup. But the two combined... I used to like it, but i've had enough. The lemon is the most important part. That's what is cleansing. You need to keep drinking the lemon water, even if you decide to skip the syrup from time to time. You can change up the amount of syrup as needed, too. I like to drink the lemon water with a dash of cayenne, and then take a tablespoon or two of maple syrup after. It all mixes in your tummy anyway.
Anyway, my lack of love for the lemonade wasn't bad enough to make me quit. I doubt you'll hate it that much either. You may even love it!