Short answer: No.
Actual ad length may vary based on:
1. When Facebook advertising permissions are granted, (will only affect your first Facebook ad order; to prevent delay make sure to grant us access immediately), or.....
2. When Facebook approves the ad (up to 24 hours).
If the ad only runs 1 day (as an example), it will still use the complete advertising budget allotted for the length of campaign you select.