I have written the following code:

public static int getDaysTillActivation() {
    ZoneId z = ZoneId.of("Europe/Berlin");
    int day = ZonedDateTime.now(z).getDayOfMonth();

    for (int i = 0; i < 31; i++) {

        if (day % 2 == 0) {
            return i;
        }

        day++;
    }

    return -1;
}

public static String getTimeString() {
    int daysTillActivation = getDaysTillActivation();

    if (daysTillActivation == 0) {
        return "Active";
    }

    ZoneId z = ZoneId.of("Europe/Berlin");
    ZonedDateTime zdtStart = ZonedDateTime.now(z);
    ZonedDateTime zdtStop = ZonedDateTime.now(z).plusDays(daysTillActivation).truncatedTo(ChronoUnit.DAYS);
    
    long millis = ChronoUnit.MILLIS.between( zdtStart , zdtStop );
    return formatDuration(millis);
}

It works, for now. But before I use it in some sort of "production", I would like to hear some advises on what could be better, or what it could break...

Here's my general Idea: I want to have a feature be enabled only every 2 days, therefore I would like to display to the user how much time is left for it to be enabled

For Example:

• Mon 30.Jan - Enabled
• Thu 31.Jan - Disabled
• Wed 1.Feb - Disabled
• .... - Enabled

As you can see, I don't mind if they have multiple days off. That's why I went with simply checking if the current day is dividable by 2.

However, this code will run every second and I just want to make sure I get everything right/get the best performance out of it.