C++ comparing current day and time with current day and set time

I'm trying to compare two time values and display time that is left till upper limit, but I'm unable to do so with my knowledge.

Basic idea:

    if(now >= (today 8:15) and now <= (today 9:45) )
        ....display "first lecture ends in" (time left)
    .
    .
    else if 
    .
    .
    else 
        ....display "short break"

I just cant find any simple examples/solutions or it's my way of thinking that's wrong. I'm distinguishing days with

tm_wday

and now I want to distinguishing time intervals while comparing time values.