Gareth,
When you say 'absence', what kind of absence are you thinking of? If it's sickness absence, then sadly you do need to enter them in chronological order, for the simple reason that they may need to be linked from an SSP perspective. The system will therefore prevent you from entering a sickness where there is a sickness with a start date after the one you're trying to enter.
I think ordinary leave absences may allow it, but you might, if there is some kind of OSP thing in place, need to approach it with a due sense of caution.
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L&K
CT
Remember: A dog is for life, not just for Christmas... unless you're in Korea