The basic explanation of the Schedule timer is - it's a basic CRON timer.
If you are unfamiliar with CRON timings, the following description of each timer field should help you determine what you need to enter, to get the result you desire.
Minute - the minute of the hour at which to run the task. Accepts any number between (and including) 0 and 59. You may also use * to denote "every" minute. You can also do things like */5, which translates to "every 5 minutes", or */30 for "every 30 minutes".
Hour - Basically the same as the minute field, however it accepts a number between 0 and 23. * denotes "every" hour. */5 would be "every 5 hours", and so on.
Day of Month - More or less self-explanatory, if you want the take to run on a single day of the month, this is the date it will run on each month. set to * to allow the task to run no matter what day of the month it is.
Day of Week - The day of the week the task will be allowed to run on, useful for tasks that should run once per week. Use * to allow the task to run no matter what day of the week it is. Accepts numbers between 1 and 7, or the first 3 letters of the day, IE: MON, TUE, WED, etc.
Some examples of common tasks would be:
0 0 * * - Will run the task once per day, at midnight.
30 12 * * - Will run the task once per day, at 1230(30 minutes past noon)
0 0 * MON - will run the task every Monday at midnight.
0 0 1 * - will run the task on the 1st of every month, at midnight.