That is not how it works. To begin with you cannot fit in favors between red scrip gathering for 11 hours, because you buy those favors with red scrips.
Let's say you first grind out 50 red scrips and buy a set of 5 favors. From this point on you can now use favors in between red scrip gathering.
However, you still cannot just fit in 11 hours just like that. You are not talking about 11 hours that can be divided, added, substracted randomly.
If you were to fit in more then two favors per Eorzean Hour you would lose out on either red scrip gathering time or favor gathering amount. Because of travelling time to each node, which takes up a few minutes each. (twice, since you also have to go back to the favor location)
In other words first you 50 red scrips would have to be grinded.
This would take about an hour. Lets assume access to the folklore node and one gathering class.
Then the remaining red scrips would have to be farmed with two favors in between. This would take about 8 hours.
Red scrips are now capped after 9 hours, and there are 29 favors left. Completing these require another 7 hours.
As such with the method you described (which you did not think through properly), it would take 16 hours to use up all favors. With a better rate of obtaining red scrips (multiple classes, or fishing), it will still take well over 11 hours just for the favors.
