When my Sim performs a task with the stove no time gets deducted from the remaining time.
The exception is the risky tasks. They work as expected but for normal tasks I need to
perform tasks with my co-worker, patrons or other kitchen area. The stove doesn't decremate
my remaining time unless it's one of the risky ones.
It' not a bug.
In the chef career some actions will give you "special objects" (food dishes) instead of a time deduct.
Then with other actions (near the tables) you will be able to serve that dishes to the clients and get your time deduct (without spending any energy).