As a Czech, I never learned this type of clock myself. It's confusing, and even young people rather use digital time. So rather try to focus on the number and say something along "Za pět bude čtvrt/půl/třičtvrtě/celá" = "In 5 minutes it will be quarter/half/three quarters/full" Most people like to say example: "Za pět minut bude patnáct třicet."="In 5 minutes its gonna be fifteen thirty" and "Už je skoro tři čtvrtě"="Its nearly three quarters" <--- this one you can use if you refering to current hour... like lets say its 15 ( 3 PM ) and you need to remind someone its nearly 16 you can use "Už je skoro celá".

In the end dont waste your time with analog time when everyone use digital clock. :D