I have used TimeTrap (https://github.com/samg/timetrap) for years. I have it installed on a dev/utility server I have hosted in the cloud. I use JuiceSSH on my android phone to run quick check in and check out scripts. While I'm at my workstation I have a terminal open that is SSHed into my VM. One of the panels in tmux is using a watch command to monitor my time. Purely just a time tracking function so I can't generate invoices or anything like that.