By changing the remaining/set time of a timer to a numerical input it would be easy to configure the runtime from Lovelace and also allow for adding time. The general behavior of the helper could stay the same but would expose this one setting in addition. Doing so should not break old dashboards and automations as the underlying actions and values are still present.
Having a slider to configure how long for eg. a motorized window should open for would be extremely useful but can currently only be done with a lot of yaml. Also this method would not show the remaining time on the slider and if this functionality is also coded into the yaml it won’t return to its default state once the end was reached with out more helpers and more yaml.