。
Up to about what time is it okay to call?
Literal
What-time about until [if-なら] phone do-[even-ok-てもいい]?
A common polite question about phone-call etiquette. The scope particle までなら ('up until X, if that's okay') marks the temporal endpoint under a conditional. 何時くらい uses くらい ('about, approximately') to hedge the exact time. ~てもいい asks permission. The sentence is polite-form throughout with ですか closing it. A perfectly natural phrasing for checking a social norm.