Let's look at the likely event leading to a decompression. In the event of window failure, B747 outflow valve (one) breaking off - yes it does happen - or a fairly big hole (QF30) you would have the worst survivable case IMHO. The cabin alt will NOT immediately be at outside alt, nothing like it. You will meet the cabin on the way down according to reports from those who have "been there and done that". Much greater structural damage and it becomes academic interest only, you're screwed and the aircraft is unflyable. If you have a total failure of the air ducts into the packs somehow, the cabin climbs quite slowly.
In reality you have more than enough time to get your sweep on mask properly fitted and commence descent without rushing things. A turning entry is to be recommended because you really don't want meal or bar carts floating around so about 25* AoB will give a little positive G to keep the carts on the floor, initiate the descent gently as the nose drops - on Boeings anyway - and get you off the airway. Don't forget to turn back parallel around five miles offset. Unless you are ABSOLUTELY certain that there is no structural damage, do not increase speed. It is reported that Boeing stated that had QF30 sped up much it would have been likely catastrophic. Also be sure that the A/P is responding correctly - the electrical wires were broken on QF30.
You will, of course, have loaded the escape procedures into the FMC at the end of your active route and also have a route copy in RTE 2 to allow for the turn back case. Having briefed your crew and yourself about the way to go and being aware of the wind - jet streams? - it is a matter of putting into practice what you have briefed. You needed to be very thorough too with the escape tracks changing frequently in the critical area. Not a time for a crew meal!
In an airline from the Great Southland, we had quite complex escape tracks for the L888 Silk Road route and the tracks over China for the LHR-HKG-LHR legs. The escape procedures for Afghanistan are simple.
L888 was a horrible concept in the worst case deco, over 20 minutes at F20.2, a few descents and still F140 when you got to your diversion port after almost three hours.