Sneezing & Watery eye

Question
My 14 year old tabby, KITTY, has been sneezing once in a while the past 2 days and his right eye is watery (not a lot, just a little).
Today, KITTY's eyes have cleared and sneezed only once..he seem better.  HOWEVER now my 5 year old cat, PRINCESS, sneezed a couple of times (but her eyes are clear).

Other than that, both are eating and purring.
How long should I wait to observe before I take them to the vet?  For now, I ordered KC-Defense which will hopefully help.

Thank you for your help.

Answer
Solita,

Do your cats have contact with other cats, for example by being indoor/outdoor cats? If so it may be wise to take them to the vet for a course of antibiotics to prevent any secondary infections that can be caused by upper respiratory infections as that may be what's going on with your cats. Since your older cat is elderly his defenses may not be what they used to be so even though it appears that he is getting better it would still be wise to have him examined by your vet in case something else is happening with his health that may not be apparent. Your five year old cat most likely has the defenses to fight this bug provided that she was properly vaccinated as a kitten. Since both cats seem to have a good appetite you may wish to take a wait and see approach with both cats, just be sure to pay extra close attention to what's happening with your elderly cat, he is roughly equivalent to a human in their mid 70s so he needs a bit of extra care, especially when he's been feeling a bit under the weather for a couple of days.