40 hours per week is probably right around the maximum a border collie can be left alone across a working week, but it is even more work for the owner.

A well care for border collie can be left home for a typical work day, but they need physical & mental exercise before you leave for work, you need to leave them with a "job" they can do around the house while you're gone (like training them to find & put away hidden stuffed animals through the day, or leaving with a smart toy), and you need to give them even more physical & mental simulation when you get home. It would be especially great if you could afford a dog walker to take them out halfway through the day.

Like I said, it requires even more commitment and hard work to own a border collie if you have a full time job. But if you are willing to put in the time and money it can be done and it can be very rewarding.

I say this as a former BC owner. Both my mom and sister still have BCs. Now, I've wised up and got a Toller :)