The WorldPay cutoff for Funding Instructions is 7pm Eastern.
There is a processing time after you approve settlements so a general rule of thumb would be to allow 15 mins for the settlements to process. As a result, 6:45pm ET should be the latest you could approve settlements for merchants to receive funding the following day.
However, if the number of settlements is large, the processing time on WorldPay side will get larger. In general, we recommend approving settlements by 6 PM ET.