Dealing with differently formatted Strings and trying to categorize their data using Java

I have a column of a spreadsheet that contains data on opening hours for different establishments. Using Java I am trying to store that data in variables (monHours, tuesHours, etc.) but the roadblock I am trying to figure out how to deal with is that there are many different ways each element is formatted. Here are some examples of variations:

"Monday – Friday: 8am – 5pm, Saturday Closed, Sunday Closed"

"Mon 7:15 AM - 4:00 PM, Tue 7:15 AM - 4:00 PM, Wed 7:15 AM - 4:00 PM, Thu 7:15 AM - 4:00 PM, Fri Closed, Sat Closed, Sun Closed"

"Monday 4AM-8PM-Saturday 4AM-8PM, Sunday Closed"

"Mon Closed, Tue Closed, Wed 7 - 9:00 AM, Thu Closed, Fri Closed, Sat 7 - 9:00 AM, Sun Closed"

"24/7"

Again, I am just trying to figure out an algorithm in Java that will take any of those strings and store the opening hours for each day in a variable. I should also note that I can't change the data to one singular format as there are hundreds of entries.

I know that it probably has something to do with string methods, specifically substrings. I have already figured that removing whitespace and commas would probably help, but I am overall struggling to find an algorithm that works for all cases.

EDIT

For example if I had an entry of a String like
> "Monday – Friday: 8am – 5pm, Saturday Closed, Sunday Closed"

I would create an array of Strings like

["Monday: 8AM-5PM", "Tuesday: 8AM-5PM", "Wednesday: 8AM-5PM", "Thursday: 8AM-5PM", "Friday: 8AM-5PM", "Saturday: closed", "Sunday: closed"].

The specific formatting of each element in the array may be different but I imagine you get the idea of how I wish to store it.

It's a complex parse.  You can start by delimiting the strings on the comma.

String[] strings = {
    "Monday – Friday: 8am – 5pm, Saturday Closed, Sunday Closed",
    "Mon 7:15 AM - 4:00 PM, Tue 7:15 AM - 4:00 PM, Wed 7:15 AM - 4:00 PM, Thu 7:15 AM - 4:00 PM, Fri Closed, Sat Closed, Sun Closed",
    "Monday 4AM-8PM-Saturday 4AM-8PM, Sunday Closed",
    "Mon Closed, Tue Closed, Wed 7 - 9:00 AM, Thu Closed, Fri Closed, Sat 7 - 9:00 AM, Sun Closed",
    "24/7"
};
String[] values;
for (String string : strings) {
    values = string.split(", ");
    for (String value : values) System.out.println(value);
    System.out.println();
}

Output

Monday – Friday: 8am – 5pm
Saturday Closed
Sunday Closed

Mon 7:15 AM - 4:00 PM
Tue 7:15 AM - 4:00 PM
Wed 7:15 AM - 4:00 PM
Thu 7:15 AM - 4:00 PM
Fri Closed
Sat Closed
Sun Closed

Monday 4AM-8PM-Saturday 4AM-8PM
Sunday Closed

Mon Closed
Tue Closed
Wed 7 - 9:00 AM
Thu Closed
Fri Closed
Sat 7 - 9:00 AM
Sun Closed

24/7

> "Again, I am just trying to figure out an algorithm in Java that will take any of those strings and store the opening hours for each day in a variable"

You can use a regular expression pattern, although I wouldn't recommend it if the format is too arbitrary.

For example, this is specific to matching only the formats you've provided.

(?i)((sun|mon|tue|wed|thu|fri|sat)(?:(?:nes|rs|ur)?day)?:? (\d?\d(?::\d\d)?(?: ?[ap]m)?))

Pattern pattern = Pattern.compile("(?i)((sun|mon|tue|wed|thu|fri|sat)(?:(?:nes|rs|ur)?day)?:? (\\d?\\d(?::\\d\\d)?(?: ?[ap]m)?))");
Matcher matcher;
for (String string : strings) {
    matcher = pattern.matcher(string);
    while (matcher.find()) {
        System.out.println(matcher.group());
    }
}

Output

Friday: 8am
Mon 7:15 AM
Tue 7:15 AM
Wed 7:15 AM
Thu 7:15 AM
Monday 4AM
Saturday 4AM
Wed 7
Sat 7

I would suggest to implement a method for each of expected formats. Each method would try to parse a string as it formatted in a corresponding way. If the parsing was successful - return the result, otherwise throws an exception (or return null, or whatever you like). Then write as many methods as there are formats you expect and execute them one by one until some method would return successfully parsed value.

Parsing is another issue, but I would create a proper data model to hold your opening times, perhaps something like the below:

import java.time.*;
import java.util.*;

public class DaySchedule {
    record FromTo(LocalTime from, LocalTime to) {}
    public static void main(String[] args) {
        try {
            Map<DayOfWeek, List<FromTo>> openingTimes = new HashMap<>();
            // Make mutable List
            openingTimes.put(DayOfWeek.MONDAY, new ArrayList<>(List.of(new FromTo(LocalTime.of(14, 20), LocalTime.of(16,20)))));
            // Add an evening opening period to the short afternoon one
            openingTimes.get(DayOfWeek.MONDAY).add(new FromTo(LocalTime.of(17, 0), LocalTime.of(19, 0)));

            System.out.println(openingTimes);
        }
        catch(Throwable t) {
            t.printStackTrace();
        }
    }
}