I have traveled I-4 for 6 years from Deltona to MCO.
It will depend on the time of a work day. 6:30 to 8:30 AM, West bound I-4 is grid lock rush hour. I would take I-4 if it were 8:30 AM to 3:30 PM. Otherwise, I would take 417. which is longer but faster. Weekends should be no problem.
Highway construction in FL is done at night. From Sanford to the attractions area there is very little construction Most of it is to the east of where you will be getting on.
If you are arriving MCO, I would always take 417 to WDW.