It sounds like you are using the default TIME_FORMAT setting, which is the US format of mm/dd/yyyy. If you add TIME_FORMAT attributes for each sourcetype in your props.conf files on your indexers and heavy forwarders, Splunk should read dates correctly. The TIME_FORMAT values should match the way timestamps appear in your data. That's probably something like %d/%m/%Y %H:%M:%S. You will need to start Splunk after editing the props.conf files. Note that the change will only affect new data; data that is already indexed will not change (you may need to re-index it).
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