spontaneous dating seems weird and inappropriate to me.
SERIOUSLY? Since much of life is spontaneous, meaning that it is unpredictable, it would be a good thing to see how each of them handles a spontaneous date. Assuming they are both free that day or evening, two hour notice SHOULD be enough time. Now, that is also assuming the two like each other and are comfortable with each other to be “chill” about it. If they are still going through a shadchan, then they have clearly not reached that point yet.
(Personally, I feel the shadchan should just speak to the boy and girl to see if they agree to go out the first time, then let the boy call the girl himself to actually make the date. I am not for this nonsense that the boy and girl cannot make a date with out a third party doing the actual work of making the arrangements between them once they have each accepted the shidduch.)