I think a week is too long. If you've both swiped right, then she's interested. Chat for an hour max (depending on frequency of messages*—if they are coming quick then 20 minutes) and then ask for her number. Another hour (same as before) and ask her out.
There might be some privilege I need to check here, but my basic logic is if she swiped right and gave you her number, she wants to be asked out. No sense putting it off. It's more fun to learn about her on a date than during texts.
*If the frequency is super slow, like a message every 4 hours, move on. The Brad Pitt rule applies here: if you looked like Brad Pitt, would she wait 4 hours? In my opinion, this is a good gauge of her interest in pretty much all things.