Great question — answering as the UphillTech team:
The receptacle covered with the two flip doors may have been legal when it was constructed, but it is now damaged and sub standard by today's electrical code. There is obvious water damage and corrosion in the photo. Code now requires an "in-use box", a WR rated receptacle, and for brick install the manufacturer will require caulking the perimeter of the cover. Considering the poor condition of the receptacle and unknown lighting connected to it, the timer is unlikely to be the main problem. If you are really just concerned about the new timer, try it on a different GFCI indoors and connect a lamp to see what happens on a separate and dry circuit.
Full answer by Robert Chapin: https://diy.stackexchange.com/a/312117 (CC BY-SA 4.0).
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