Less than a month, possibly (or a bit more, if you plan on prematurely-optimize it for instagram-level traffic - which will possibly never happen for the "clone

Less than a month, possibly (or a bit more, if you plan on prematurely-optimize it for instagram-level traffic - which will possibly never happen for the "clone" anyway). The hard part, really, would be BECOMING Instagram. The software is pretty much trivial (as was Facebook at the beginning)...