If what you call the whole hour is comparing with something like 17:34:22 (for 17h 34min 22 sec) then best is to convert that into seconds since midnight
const unsigned long startTime = 17*3600[color=red]ul[/color]+34*60+22; // note the ul to avoid integer overflow
Imagine you have a stop time at 19:33:47
const unsigned long stopTime = 19*3600[color=red]ul[/color]+33*60+47;
Then read the current time in seconds since midnight
DateTime now = RTC.now();
unsigned long t = now.hour() * 3600ul + now.minute()*60 + now.second();
And you can see if you are inside or outside the [startTime, stopTime] interval with
if (t>=startTime && t<=stopTime) {
// here you are in the interval
} else {
// here you are not
}
If you want to take into account the exact day in the calendar you can use unixTime