Saturday flight YYZ to FLL
 

Flight scheduled for 6:40 am.Traveling with wife. Both have NEXUS. Wife uses walker. 5:15 am at the airport would be good enough to make it to the gate in time at T1? Thank you.

I would go earlier if possible. If flight is scheduled at 6:40, boarding will likely start at 6AM, meaning you'd only have 45 minutes to go through US CBP, security and then to your gate. Nexus lines can have lines too, albeit much shorter, add in a walker, you're just asking to be stressed out. This is assuming you're travelling strictly with carry-on luggage. If you need to check anything in, I would say it's almost impossible.