Late to the game...

If you want to spend some time out of the airport - go to Oriente. It's a 10-min Uber ride, and will give you enough time to enjoy some river views and have a coffee and a Pastel de Nata.
P.S. Twice I've done a 90-min connection on 2 separate tickets that required me to take an uber home, drop my bag, change clothes and be back at the airport. I was living around Saldanha at the time. This was totally doable and both times I even had time to spend at the lounge for a quick bite to eat.

4h45 - the critical time is passport control. Once you're past you can decide if it's worth it.

Ideal conditions:

L+0h15 (T-4h30) - off the plane
L+0h60 (T-3h45) - through passport control
L+1h30 (T-3h15) - in downtown
L+3h15 (T-1h30) - depart downtown
L+3h45 (T-1h00) - arrive at the airport

This gives you 1h45 to enjoy the city ASSUMING everything's perfectly on time and you don't get delayed anywhere. You decide if it's worth it.