I think you shouldn't feed dd#1 just before dd#2, as far as I researched it should be the other way round. But, don't worry if you miss feeding her in a day, that shouldn't affect your supply so much. Women who tandem nurse, usually nurse their older children many times a day and it is also not on schedule so they breastfeed 8 times one day and 3 the other. And they still manage to do fine with nursing their youngest nurslings.
There is a good book on that, if you have time to read it, I recommend it. It is"The Adventures in Tandem Nursing", if you would like it, I will find an author :lol:.
Good luck,