All those hours and for what?
Statistically, there's only a 25% chance to get to a chain of 20 from 0, and a 5% chance to get to a chain of 40 from 0. And eevee has a 5% appearance rate in this garden. So I find it more worth my time to reset for a while on a chain of 20.
I also found both a shiny roselia and porygon in the same garden while looking for eevee, on the first grass of the chain, which was cool.