Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 191; Flight Crew Type 191
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory
Company Policy; Environment - Non Weather Related; Procedure
Prior to takeoff; I informed the flight attendants that I would like them to remain seated until cruise altitude due to the weather in the ZZZ area.  We pushed off of Gate and took off on Runway X.  Prior to takeoff I notified the flight attendants with a 'ding' and observed their response; over the PA; that we had been cleared for takeoff and completed the Before Takeoff Checklist.  As expected; we encountered light turbulence during the climbout to cruise altitude.  Passing FL350; the flight attendants 'dinged' us and asked us if it would be OK if they got up.  At this point they informed me that they had not completed the oxygen demo briefing and that they would like to get up and do it.  I agreed that yes it needed to be completed and they did.  I said that we would talk about what had happened and why when we landed.  Once in (city); I asked them what had happen.  They said that in the middle of their briefings some passengers required some attention and put them behind.  It took six minutes from pushback to takeoff.  Once they had the situation solved; I 'dinged' them and they agreed amongst themselves that they would complete the oxygen demo brief after takeoff and below 10;000 feet.  I didn't know we could do that; but they said they could.  At that point they made the cleared for takeoff brief signaling to me that they had completed their cabin preparation and were ready for takeoff.  After hearing their story; I explained to them that 1) had they continued the oxygen demo brief after I 'dinged' them; I would have known they were not ready and would have delayed the takeoff; or 2) don't make the cleared for takeoff briefing and contact the flight deck and let us know that they required additional time to prepare the cabin due to some passenger issues.Although the First Officer and I were unaware of the situation until passing FL350; this event could have been avoided if the flight attendants had a better understanding of our procedures and if the pilots were more consistent in applying the Before Takeoff Checklist.  As I explained to the flight attendants their options prior to the event; why we 'ding' them and what we expect to hear to continue with the takeoff; they said that they didn't believe that all pilots would have waited for them to complete their duties.  They felt or believed that some pilots just hit the call button and takeoff without even monitoring the PA.  So possibly a Crew Briefing Bulletin emphasizing our before takeoff crew procedures and the importance of the flight attendants' duties being completed prior to takeoff and the pilots verifying that they have been completed.
[Narrative #2 contains no additional information.]
A B737 took off after a six minute taxi during which time flight attendants handling a passenger issue were unable to complete the oxygen demo and because of turbulence remained seated until FL350 when the oxygen demo was finally completed. The flight attendants failed to notify the Captain about the oxygen demo situation until cruise.