Add setting "SpentTime required" into section "Time tracking" on the "Administration - Roles - CertainRole" page.
If this setting is set, then user with this role in the project will have to specify spent time when trying to transite task into one of states, specified in plugin preferences.
In case when a person is assigned several roles in one project, it would be more correct to look through all his roles and ask for spent time only if ALL roles have setting "SpentTime required" checked.
Add setting "SpentTime required" into section "Time tracking" on the "Administration - Roles - CertainRole" page. If this setting is set, then user with this role in the project will have to specify spent time when trying to transite task into one of states, specified in plugin preferences.