So here's the plan

I arrive on NH818 from PNH at 6:45
I'm guessing 90 minutes to process customs, then take N'EX Tokyo to Shibuya
That would have me at Shibuya around 10 AM
I plan to spend 3 hours and then at 1 PM head back to NRT to and be at the airport at 3 PM for my 5 PM flight to SFO

My bags will be tagged all the way so only carry on that I plan to leave in a locker

Is it too crazy or doable?

Thanks