I'm contemplating doing 3 back-to-back multi-segment transcontinental mileage runs next month (never quite done that before). The question is how much slack time to leave in case of delays.

Flights are NW SEA-DTW/MSP/MEM-FLL (not the cheapest but it works; I have lounge access and potential for UGs) and $50-off ECVs per trip). Turnaround at FLL is about 1-1 1/2 hours (arrive mid-late AM, take late A to early PM flight getting into SEA early PM). How much time should I leave at SEA for the turnaround? One whole nighty, or just a few hours? No home to stay as it isn't my homeport.