Swelling is a natural occurrence after a surgery such as this. Your doctor cut into your knees, cut into your bones, removed them and added new implants. All that caused trauma, and your knees are now in recovery mode from the abuse that is a TKR. The tightness is a result of swelling, both internal, which you can't see, and external which you can see. Even if your knees haven't yet begun to swell visibly, they are swollen on the inside and will likely begin to swell on the outside at some point.
Doing PT this early will only increase the irritation to your knees. If you do decide to do PT, I suggest you keep it to gentle motions and some walking for now. But, if you choose not to, which is your right, then you have the right to cancel the appointment.
https://bonesmart.org/forum/threads/saying-no-to-therapy-am-i-allowed-to.36688/
Don't allow the therapist to push or pull your knees to try to force a random ROM number; not only will it cause your knee more distress, but any number achieved by the therapist forcing your knee is not a true number. Only that which you achieve on your own without being forced is a true number. But in these early days. I wouldn't even worry about ROM; until your knees settle down from the trauma they just went through, you won't see a ton of bend.
Over time, as your knees settle down, your ROM will improve, but forcing it, or heavily exercising them to try to force a bend now is counter-productive. Your new knees are in there, ready to bend, as soon as your tissues, etc, recover. For now, a lot of icing and elevating, and some walking around your house, along with some gentle stretches, are all that's necessary. Over time you'll begin moving around more, and adding more activities.
https://bonesmart.org/forum/threads/activity-progression-for-tkrs.14334/