Installation failed: Timeout was reached: Operation timed out after 10000 milliseconds with 0 out of 0 bytes received

 Trying this option worked for me.

 library(httr)

 with_config(use_proxy(...), install_github(...))

 OR

 library(httr)

 set_config(use_proxy(url = "******_", port = "_*"))

 devtools::install_github("username/packagename")