You may just need 4 different relationships between the same two tables or even one relationship with 4 different portal filter expressions. A category field in your table of Time entries can be used to identify whether a given entry is Transcription, Hourly, Piecemeal or Other. This can be a match field in your relationships.
To get multiple, separate, relationships between the same two tables, you create additional Tutorial: What are Table Occurrences? of the portal table in your relationship graph.
Thank you! I knew there had to be a better way. I'm off to read your post on occurrences and cross-reference that with what the manual has to say. I had a feeling I could create multiple relationships, but I couldn't figure out how.