Alright, I got Saturday as well, so lets take a crack at it...
Today is Friday, and if it is tomorrow's yesterday it means it's still friday (goes forward and backward a day)
Since it is still Friday, we simply go back one, as that would be the day before today, therefore it is Thursday.
So then from Thurday, we move ahead two spaces, as yesterday's tomorrow is still Thursday, and thus we move ahead by two days. Leading us to Saturday (Thursday, Friday, Saturday).
If the argument is that by not stating day before today (and instead stating yesterday's tomorrow", and instead should go two days from friday as opposed to thursday, than that's not really that clear, as each day is defined as the next... "and tomorrow's yesterday was the day before today" meaning that tomorrow's yesterday is also the day before today...
Meh, I think that makes a fair bit of sense.