This is a step-by-step guide on how to create a single day absence, with two leave reasons and two segments: one with a half-day substitute and one no substitute required.
1. Create a single day job with two absence reasons.
2. Following step 7 in the link above, use Child Jobs link and Parent Jobs link to toggle between the segments. Click Assign to assign a substitute to the desired segment and Switch to Not Required on the other.