We would suggest that the system would be able to process project hour journals in the "Project management and accounting" module in D365 F&O as efficiently as possible. If a journal of +5000 lines would be processed more efficiently if split in 15 journals, and run in batch, we would recommend the system would process the job in that way. Hence, when a user initiates the posting of a journal, the size of the journal should have a minimal impact on performance.