file.java

public class Timer {  
  
    public static long parsePeriod(String period) {
        if (period == null || period.trim().isEmpty()) {
            throw new IllegalArgumentException("Invalid period - '" + period + "', is empty");
        }

        period = period.trim();

        String[] split = period.split(" ");

        long value = 0;
        Set<Character> types = new HashSet<>();

        for (String one : split) {
            if (one.trim().isEmpty()) {
                continue;
            }

            one = one.trim();
            char t = one.charAt(one.length() - 1);
            int k = 1;

            switch (Character.toLowerCase(t)) {
                case 's': k = 1000; break;
                case 'm': k = 1000 * 60; break;
                case 'h': k = 1000 * 60 * 60; break;
                case 'd': k = 1000 * 60 * 60 * 24; break;
                default:
                    if (!Character.isDigit(t)) {
                        throw new IllegalArgumentException("Invalid period - '" + period + "', at '" + one + "'");
                    }
            }

            String num = one;

            if (Character.isDigit(t)) {

            } else {
                if (!types.add(t)) {
                    throw new IllegalArgumentException("Invalid period - '" + period + "', at '" + one + "' that duplicates '" + t + "'");
                }
                
                num = one.substring(0, one.length() - 1);
            }

            try {
                double v = Double.parseDouble(num);
                value += Math.round(v * k);
            } catch (NumberFormatException e) {
                throw new IllegalArgumentException("Invalid period - " + period + ", at '" + one + "', " + e.getMessage());
            }
        }

        return value;
    }
}