The factory is a place which is unlocked at level 6. You can use the factory to upgrade items so that you can decrease delivery time and increase revenue and stock, at the cost of certain materials or money.

These are delivery comparison.

Basic Item 1st Upgrade 2nd Upgrade 3rd Upgrade Fully Upgraded
10s 9s 8s 7s 5s
20s 18s 16s 13s 10s
30s 27s 24s 20s 15s
1mn 50s 40s 30s 20s
2mn 1mn 40s 1mn 20s 1mn 40s
3mn 2mn 30s 2mn 1mn 30s 1mn
5mn 4mn 3mn 2mn 1mn
10mn 9mn 8mn 7mn 5/6mn
30mn 25mn 20mn 15mn 10mn
45mn 38mn 30mn 22mn 15mn
1hr 50mn 40mn 30mn 20mn
2hr 1hr 40mn 1hr 20mn 1hr 40mn
4hr 3hr20mn 2hr40mn 2hr 1hr20mn