If the kittens poop looks good then it's not necessary, I can't see it being detrimental in any way if they have some - it balances out the water level in the bowels so if they have diarreah it will firm them up abit & if they are consipated it will provide enough moisture to bring it back to the right amount.
1/4 tsp twice a day is a good place to start, you can always increase/decrease as necessary. My grrl gets 1/4 tsp twice a day & is a good amount for her.
You can also freeze portion sizes in ice cube trays & then dump them into a freezer bag for when you need them. Leaving the squash in the jar in the fridge it will go bad w/in a few days, so by freezing you can save the remainder. Then you can just warm it abit in the food (place the dish in hot water in the sink) before serving.
The unopened jar should have a best before date, if you don't think you will use it up before that date you can always either return it or open it a couple of days before the date & freeze it.
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food