Instagram launched in 2010 (but really gained traction only in 2011). It has been available via the web since 2012 but it took until 2015 for the web version to reach feature parity with the app version (namely posting and discovery).

Based on that, I think it's safe to assume that a full featured web version of Threads should be up within a year. Threads already has some web presence (you can view threads and profiles).