会儿 is almost always used with 一 as 一会儿 (yíhuìr). It means a short period of time. Can also be used in the pattern 一会儿...一会儿... meaning 'one moment...the next moment...' to describe something changing.
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会儿 with erhua is standard in northern Mandarin. In southern speech or writing, you may see 一会 (yíhuì) without the 儿.
