Extend the timefilter to have a UPDATED timefilter, so that you can retrieve all accounting items that have been created/modified within a certain timeframe.
This way you can easily fetch for example "give me all items that were changed since yesterday".
Advantage: If you would like to know if there were new accounting items modified/created since the last time you checked, you do not need to get all items for the entire future. That would save a lot of bandwidth and processing (on both server/client side)
This is exactly the same question as https://feedback.mews.com/forums/932131-mews-open-api/suggestions/44208861-accounting-items-createdutc-updatedutc-api-cal
outletItems/getAll should also have this timefilter for exactly the same reason.