There are several reasons for this:
- You need not only to complete the order in time but also to collect rewards in time! The remaining time is highlighted in blue.
- Rewards for express workshop orders are already doubled. Thus, you will get 104 reputation points, not 208. Their number doesn't increase if you complete the order much earlier than the end of the timer.
- Chest and diamond rewards aren't guaranteed. Their drop probability is shown as a percentage.