Simple answer: anywhere between 190-240 F is normal temp range for engine oil, depending on the situation (highway cruising at 190F, rock crawling/autocrossing at 240F)
Less simple answer: Just about any modern engine oil can handle 300F for 20 minutes. So my answer depends: what kind of oil, driving habits, drive duration (reaching full temp every time?), sump capacity, service interval, etc. And remember, when pushed hard, synthetic oil handles high temps better than conventional oil, although today's conventional oil is excellent also.