When?

When: Interrogative Adverb.
At what time; how soon

Soon: Adverb.
In or after a short time; early

Shortly: Adverb
In a short time; soon

Now: Adverb
At the present time or moment

Anon: Adverb
Soon, shortly

When we ask the question "When would you like to come in for your prescription?", we are trying to plan our day in the most efficient manner in order to ensure your prescription is ready by your intended arrival time. It really makes no sense for me to work on your prescription right now if you intend to wait until tomorrow, or the weekend, to retrieve it. This allows me to dedicate my time and energy to high priority prescriptions such as antibiotics and ER/post-surgery medications and, well, flu shots. When you have a prescription that requires urgent attention, you can appreciate all the other patients communicating honest pickup times with us.

In the question "WHEN?", we are asking for a time. It can be exact or a ballpark estimate. The correct answer to "At what time would you like to pick up your prescription?" is NOT "later"; nor is it "soon", "shortly", or "today". Those are not times on my clock.

If you choose to give me vague answers, I shall try to out-vague you.

Pt: (on the phone) Did you receive my prescription(s) from my prescriber?
CP: We did. They just arrived in my queue but we have yet to process them. "When (at what time) did you want to come in for them?"
Pt: As soon as they're ready.
CP: Okay. We will see you then.
Pt: Wait. When will they be ready?
CP: Oh. Anon. <click>

or

CP: When did you want to come in for them?
Pt: Later.
CP: Okay. See you later, alligator.
Pt: How much later?
CP: After a while, crocodile. <click>

Yes. This is an endless debate.
How do we phix it?
As I stated, we get the patients to commit to a time.
When they are vague, we give them longer-than-necessary estimates. However, this rarely works because, regardless of the time (15 minutes from now or 4 hours from now) there will always be the incredulous "That LONG!?" response. Look, if you had pinpointed a time as I had offered, I could begin work on your prescription and it may be done quicker. Since you left the time entirely up to my discretion, I made a decision based on my needs at the moment. Accept it and move on.

When people are in the store, I give them exact times if they choose to wait. In this way, there can be no ambiguity surrounding the Time Of Promise Pickup:
"If you're waiting, that'll be 22 minutes which puts us at 3:57. See you then." It helps, especially since our perception of 22 minutes differs greatly from that of the people on the other side of the counter.