The way I see it, this makes multi-classed casters a lot less stressful to play in the long-run, since their buffs tend to run out quickly. If you were to make, say, a level 10 fighter / 10 wizard, for example, it was stressful during the previous system, since the buffs would last for half the amount of what a level 20 wizard would cast. If you maximized the time you had with your spells (aka resting only when the buffs go out), by the time you rested 3 times as the level 20 wizard, your 20 hours you had to wait were gone. However, the level 10/10 caster would be stuck with many hours to go, becuase he had to rest twice as much as the wizard.
Now with the system, the 10/10 person's buffs last for 16 minutes (26 if he extends), which means that after the buffs run out, he actually can rest.
Now before anyone goes "That's unfair", they should consider that this means that level 10/10 person doesn't have to rush so much to get his job done.