Unless you are attending training, deadheading or are on reserve, you must be free of all duty on calendar day 7. I doubt "legal to start" would apply.
From ALPA's Guide to Flight and Duty Times:
III. SEVEN-DAY REST REQUIREMENT
The rule has a requirement that flight crewmembers engaged in scheduled air transportation be given 24 consecutive hours free of duty every seven days. This requirement extends to regional operators. These provisions [FAR 121.471(d) and 135.265(d)] read:
FAR 121.471(d) provides:
Each certificate holder conducting domestic operations shall relieve each flight crewmember engaged in scheduled air transportation from all further duty for at least 24 consecutive hours during any 7 consecutive days.
FAR 135.265(d) provides:
Each certificate holder shall relieve each flight crewmember engaged in scheduled air transportation from all further duty for at least 24 consecutive hours during any 7 consecutive days.
In interpreting this provision, the “seven consecutive days” are calendar days while the “24 consecutive hours” are only 24 hours, which may extend over two calendar days.
The FAA has consistently interpreted this provision to be a flight-time limitation, not a duty-time limitation. Its purpose is to insure that a flight crewmember is adequately rested prior to flying as a crewmember in scheduled air transportation. Therefore, this provision is violated only if the crewmember is used in scheduled air transportation without having had relief from duty for 24 consecutive hours during any seven consecutive days.The following are some of the frequently asked questions concerning this provision.
Q-38. If I am scheduled to fly for six days, can I be scheduled for training on the seventh day?
A-38. Yes. An air carrier is permitted to assign a crewmember to training or other non-flight (duty aloft) duties without first giving 24 hours free of duty. However, before the air carrier can again use the crewmember in scheduled air transportation, you must be given 24 hours free from all duty.
Q-39. If I am scheduled to fly for six days, can I deadhead as a crewmember on the seventh day?
A-39. Yes. However, after the deadheading, 24 hours of rest would be required before you could be returned to flight duties.
Q-40. Can I deadhead on Day One and be scheduled for flight duties for the next six days? 16
June 2004
A-40. No. The flight crewmember could not be assigned flight duties on the seventh day because the seven-day period does not contain 24 hours free of duty.
Q-41. Can I be assigned four days of training followed by three days of flight duties?
A-41. No. As in the above example, the seven-day period did not contain 24 hours free of duty.
Q-42. Can I be assigned to reserve status during a 24-consecutive-hour rest period?
A-42. Yes. Duty as provided by FAR 121.471(d) does not include time spent by a flight crewmember in reserve status and a crewmember may be assigned to such reserve duty on the seventh day providing you are not actually placed on duty aloft. Before you could be given a flight assignment, you would have to be given 24 hours free of all duty.
