the rule uses stringtotime to convert the date to a time stamp.
NOTE: the format of your date (using a slash as the separator) indicates to the string to time function that the date is US formatted(mm/dd/yyyy), but your format is using UK formatting (dd/mm/yyyy)
When using UK date formatting, use a hyphen as the separator instead to indicate the UK date format to the stringtotime() function. this format will fail:
or better still use:
Dates in the m/d/y or d-m-y formats are disambiguated by looking at the separator between the various components: if the separator is a slash (/), then the American m/d/y is assumed; whereas if the separator is a dash (-) or a dot (.), then the European d-m-y format is assumed.
To avoid potential ambiguity, it's best to use ISO 8601 (YYYY-MM-DD) dates or DateTime::createFromFormat() when possible.