Exit stamp
So, for future reference, I was able to get my exit stamp in ADZ.
Connections from El Dorado to Puente Aereo were also quite a breeze. My inbound flight arrived really early in the morning, so I had something like a 10 minutes wait for the bus in a not-so-nice area of the new terminal, but it was ok. On the return, around 8pm, the transfer was quite strait forward.
In the end, I found San Andres a wonderful destination and I was glad to have taken the decision to stay there a few more hours (and, then, have a more comfortable connection PA to ED).