I have a great deal of past experience in dealing with the OP's problem, dating from the time that I had a career and had to attend many social functions. I didn't know about HFA or AS at the time, but was very aware that I could only take so much party atmosphere (particularly noise and brouhaha), or even small talk after a dinner party.
I developed many strategies for coping, mostly by finding an acceptable opportunity/pretext for temporary escape. Mostly I didn't announce that I was absenting myself; I just slipped away for a while. If the weather was reasonable, I might go outside where it was quiet. If asked where I was going or what I had been doing, I would simply answer something like it was nice and cool outside, the flowers in the garden smelled great, or I was checking out the stars. If there were children there, particularly smaller ones, another tactic that I used was to go and visit with them. I adore kids and get along great with them, and interacting with them is very relaxing (like pets I guess!). Instead of being perceived as weird for wanting to escape from the noisy crowd, this generally comes across as being sweet for thinking of the kids. Apart from temporarily escaping, I almost always stayed on the fringes of a party, in a quieter room with fewer people, and I often left early.
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When asked why I was there I said I needed some quiet time, but apparently that's strange?? Do people think you're weird or creepy for doing stuff like this? How would you react?
I don't believe that I have ever been called weird or creepy, despite the many times that I escaped from social situations. I think that this is because I am not vulnerable, and don't appear vulnerable. People call others creepy only when they sense they can get away with it, not just because they are different. In hindsight, I realize that I would never tell anyone that I needed "alone time" - that would be projecting weakness, which I have always avoided at all costs.
If someone did call me creepy, I am sure that I would not be angry, intimidated, or abashed in any way (I care very little about others' opinions of me). I would probably nip such a comment in the bud with a simple, calm statement such as: "I guess some people just don't appreciate celestial beauty" or "floral aromas" or whatever, bearing in mind that I haven't told them that I needed "down time".
As a prologue, I would note that I put with and coped with a lot because I believed that I needed to earn money to live. As soon as I was financially able, I escaped such social gatherings permanently and now live alone, socially isolated, in a nature reserve, and I love this life.