My NYer opinion....WAY too much to do...
Is this a weekday or weekend day?
All that being said, Radio City and Rockefeller Center are 'walk by's' as in, you aren't actually doing anything other than photo ops, I assume. Top of the Rock could take you 1-2 hours depending on number of people there.
NBC Studio Tour also likely 1-2 hours.
(both 'longer end' time guesses...but btwn waiting in lines, bathroom stops, gift shop stops....you get the picture!
As you are going to the Fire Zone, Build and Bear and FAO Schwartz, I'm guessing you have young children.....which makes everything take longer
Build A Bear on a weekend day will be mobbed....
Ellens Stardust Diner....LOUD, LOUD, LOUD and without a reservation, you can wait in line outside for up to an hour. They will take reservations, of sorts, for parties over 12, I believe. In fact, I was there with a large out of town group in Feb and Bob was the manager...great guy....call him if you have a large party (or even small...who knows, Disney pixie dust might be smiling down on you that day)
So, my two cents....you have A LOT going on in one day....assuming young children...I think they will crash and burn (and Ellen's might just push them over the edge!
If I were to leave some things out, I'd leave out Build a Bear....just one more thing to carry home and you will likely have Disney stuffed things.....ditto for FAO Schwartz.....and as much as Ellen's is fun, unless you know your children can tolerate a lot of stimulation, I'd pass on that, too!
How old are your children? Central Park Zoo is wonderful and easy. Nice escape from the city.
Just my 2 cents.