As an aside, it looks like there is a MAD-VIE sector out of T4S tonight (IB3124) because EC-NJU due to operate it is doing the inbound from LHR. I presume therefore that OP's flight may be similar, and depart from the intra-Schengen M gates at T4S. Rare but not impossible.

In that case absolutely add even more time on to take the train back to T4S.