I have 3 tanks running 130g, 55g and 46g bow front, plus a 45g for a QT (which is currently dry).
Of course it takes more time as you have more tanks, but I do not feel it doubles or triples the time. I do everything for all the tanks at once (testing, top-offs etc.) except for water changes (I have to stagger them).
I like having more than one tank as I have more choices in livestock. One is SPS dominant with tangs, one has softies and the third contains livestock that is not "reef safe". The last tank started out when we bought a Sally lightfoot crab and a chocolate chip star and THEN read that they are not safe. We call it the "OOPS Tank".
The biggest hassle I feel is having so many tubs of Saltwater mixing to handle the water changes, seems I always have a tub or two mixing (especially when something is in the QT), and also needing to have some fresh RO/DI for top offs.