Completely Useless

After I dowmload the app and pay for it, it tells me that the multiply and divide buttons cant be used with dates and times. I know that I swam for 30 minutes at a rate of one minute and seven seconds per 50 meters. Simple division should tell me how far I swam. Im not sure what the point of this app is if it cant divide dates and times.

Moburgers about DateTime - Date and Time Calculator, v1.1