Converting seconds to hours, minutes and seconds
Your usage of auxiliary functions is not consistent: Some computations are
done inline, e.g.

int hours = totalSeconds / MINUTES_IN_AN_HOUR / SECONDS_IN_A_MINUTE;


and other (equally simple) computations are done using the functions
hoursToSeconds() and minutesToSeconds().

But my main point is that the calculation is too complicated, and extending
it to more time units (e.g. days) would make it even more complicated.

It is easier if you compute the lowest time unit first (seconds)
using the remainder operator %,
and then proceed to the higher time units (minutes, then hours).

Then you don't need additional functions for the conversion and therefore you
can restrict the scope of the conversion constants to 
the timeConversion() function.

private static String timeConversion(int totalSeconds) {

    final int MINUTES_IN_AN_HOUR = 60;
    final int SECONDS_IN_A_MINUTE = 60;

    int seconds = totalSeconds % SECONDS_IN_A_MINUTE;
    int totalMinutes = totalSeconds / SECONDS_IN_A_MINUTE;
    int minutes = totalMinutes % MINUTES_IN_AN_HOUR;
    int hours = totalMinutes / MINUTES_IN_AN_HOUR;

    return hours + " hours " + minutes + " minutes " + seconds + " seconds";
}