You can add one-click timers in your custom sidebar by typing text into the input after choosing the "One-click Timer" item type.  Depending on what text you enter, you can create hourglass timers, tomato timers, and repeating tomato timers.

If you use a simple time duration, like 10m, then clicking the item in your custom sidebar will start an hourglass timer. 

If you use two time durations separated by a slash, like 10m/5m, then clicking the item in your custom sidebar will start a tomato timer (in this case, 10 minutes of work time followed by 5 minutes of break time). 

Similarly, if you add another slash and a count, like 10m/5m/3, then clicking the item will start a 10m/5m tomato timer that repeats (running a total of 3 times).