It doesn't matter if you have 250 or 2500 hours...when you are an airline first officer your ability to safely fly, manage, and land the airplane by yourself if the captain becomes incapacitated should NEVER be in question. If you can't be relied on to do that solitary function, you absolutely do not belong in that seat.

Some folks at 250 hours or 500 hours or 1000 hours have the skill, knowledge, experience, situational awareness and calmness to accomplish that...but some don't.