It is not recommended to drive more than a certain time in recirculation setting - you risk getting drowsy without getting fresh air. IIRC that's about 20 minutes.
Yes normally, in Auto mode, the recirculation will revert to fresh air when the interior cools.
However, if the outside temperature is too hot for the capacity of air conditioner to reduce the interior temperature to the temperature setting, i.e. the temperature down demand required exceeds the capacity of the air conditioner to chill the air, then the system will sit in recirculate.
The way in overcome this is to increase the temperature setting in Auto slightly to the point to which the air conditioner can cope with the demand i.e. the system can automatically switch to fresh air.
In other words, if your temperature setting in Auto is too low, you will be demanding more chilling capacity than the air conditioner can supply.
The interior may be slightly warmer than you might normally chose but you will get fresh air. The air conditioner will be operating at maximum capacity.
As said, you can manually over ride the recirculate, which is much safer than driving for a long time in recirculate. You will get fresh air but it will not add to cooling as the air conditioner will still not have the capacity to chill to your desired setting. In fact it may well increase the overall internal temperature.