4 hours would be a paid day for you as a part timer
For FT drivers, my paycheck showed this last May
VAC - 3.00 w
OPD - 24.00 h
OTH - 40.00 h
Means 3 weeks vacation, OPD (optional day(sick)) was 8 hr x 3 days, and OTH was my optional week (the remaining 5 personal and sick days) 8 hr x 5 days