Q. When not able to step back due to people davening behind you, is there a shiur of how long you are mechuyev (obliged)  to wait.
A. Horav Shlomo Miller’s Shlit’a opinion is that one should wait the normal length of what most of the people in that shul take for finishing a regular Amidah. Alternatively, if possible and when needed, one may step back sideways. (See Shulchan Aruch O.H. 102: 5 – 123: 1-2).
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a