I find that instant dates are quite rare because during the day most girls are out with a plan to do something like meet friends or go to work or go buy sex toys or something. But if she has time, isn’t in a rush, and you are building a comfortable attractive connection with her you can easily ask her to come on an instant date with you.
First tell her you something important to do within half an hour. Just in case she worries you want to spend a long time with her. Make is seem completely casual and short term. It will be short if there is no chemistry between you two, but it will go longer if you have an awesome interaction together.
Then tell her you were about to go get an icecream/coffee/tea/fruity drink/piece of cake/ whatever and since she seems interesting it would be cool of her to come along with you and continue the chat. Ideally it is a place very near to where you are talking to her and visible from where you are standing as it makes it seem more reasonable. Also notice that you can qualify her at this point and let her know she is getting the chance to go on an instant date with her because she meets one of your standards.
Then you’ll need to lead the interaction. Don’t ask her to come along, but tell her she can come with you, and then start walking. She will follow. Take responsibility of making the decision, you don’t need her permission. The ONLY reason she wouldn’t follow you is if she is legitimately busy or if you haven’t built any attraction and trust yet.
That said, She can still say no if she really wants to, and so you smoothly have a reason to go for a number and reschedule another time to have your little date.
Going for daygame instant dates can help you get laid whether you actually get the instant date or not. Always go for the instant date and if you don’t get it number close her and arrange a date for another time.