It really depends on when your free. You have already made the first contact so thats not a problem anymore. Don't contact her today if you haven't already. If she contacts you, usually asking how you are (boring), thenreply with something like "Hey, Im good thanks. Really busy though! Hope your well. Ill text you tomorrow or something when less busy" By saying something like that it's giving you the power AND your not going to be thinking if shes going to reply or text you cause you've told her you would when you can.

Your next message should be to the point though. You could text with something random first and after the reply ask her out or with a "Hey, hope your well" THEN go into the asking out part all in your first message.