Configure predefined tmux windows

For quiet some time now tmux has become one of my day-to-day core tools. With time I also adopted and refined a set of tmux windows I create everyday to keep my tools sorted (like a window for timetracking for example). So why create these windows everytime I start tmux? There should be a way to configure these once, right? And actually there is a pretty simple way. So simple even that it made me…