A: "Excuse me. Do you close at 8 o'clock this evening?"
B: "No. I'm afraid we close at six."
QUESTION: Isn't it (#A) supposed to be the present continuous since 'this evening' is mentioned?
ANSWER: No, both can be used as the #A's question, since the time adjunct "this evening" is not a factor here:
- A: "Excuse me. Do you close at 8 o'clock this evening?" -- (simple-present, as in the OP example)
- A: "Excuse me. Are you closing at 8 o'clock this evening?" -- (present-continuous)
It would seem that for most expected types of contexts, that either the simple-present version (#1) or the present-continuous version (#2) would be fully acceptable.
Though, it is possible that a specific context and the speaker's intent, or frame of mind, can make one version more probable than the other. For instance:
If the speaker is in a bad mood, or in a hurry, or is trying to sound concise, etc., then the speaker might tend to use the shorter simple-present version (#1).
If the speaker is trying to be polite, or be more polite, or wants to put more attention onto the actual expected time of closing which might be different from what it would normally be, etc., then the speaker might tend to use the longer present-continuous version (#2), or even possibly a longer version such as, #3.) "Excuse me. Are you going to be closing at 8 o'clock this evening?" which uses the "BE going to Verb" construction.
Note that the above considerations also apply to #B's possible responses, such as:
B: "No. I'm afraid we close at six." -- (simple-present)
B: "No. I'm afraid we are closing at six." -- (present-continuous)
And of course, there can also be even longer forms, such as:
- B: "No. I'm afraid we are going to be closing at six." -- ("BE going to Verb")
NOTE: There are some types of situations where it might be preferable, or expected, to use a simple-present tense over a present-continuous, and vice versa. But this whole topic of one versus the other is rather large and involved, and it's better to discuss a specific situation than to try to cover the whole topic in one post.
ASIDE: There's a lot of info out there on the continuous (i.e. progressive) construction. It is not possible to explain the ins-and-outs of that topic in a handful of pages or in a few short lessons. Linguists are still arguing and disagreeing on many of the involved issues. Anyway, here's one tidbit that is somewhat related to the OP's post -- an excerpt from Change in Contemporary English, by Leech, Hundt, Mair, Smith, paperback published 2012, page 140:
- Thus in (51), I will not be taking part is likely to come across as more tactful -- less like a forthright refusal -- than I will not take part, I'm not going to take part, etc.
Notice how the longer version "I will not be taking part", with the continuous "be taking", is considered to be politer than the shorter version "I will not take part".