Persistent Thrust Extended is a plugin that allows you to use your engines during timewarp, allowing you to speed up a burn that would take days down to a few seconds.
Ever had to make a burn that required several minutes or longer at high physics warp but it still took too long? Want to maximize your deltaV but don't want to spend hours performing a burn? now you can with Persistent Thrust. All you need to do is set the SAS mode, set throtle and activate timewarp (upper left of screen