Workout = How many calories?

RosieWest8

I'm new here and am just wondering if there's a general consensus on how many calories one should burn while working out.

I usually just think about time spent exercising instead of work done/calories burned while exercising. And I have a new treadmill that has a calorie counter (that I can't turn off)...so it's just there right in my face. =D So when I work out (walking on an incline, sometimes jogging for a few minutes, then walking again) for my time (25-40 depending on how I'm feeling that day) I usually burn about 300 calories (according to my machine)....

...is this a good amount to be doing with a workout, just once a day? Or should I be trying to do more when I'm working out?
I have a weird schedule at work so getting in the 25-40 minutes fits right in....I don't really have and hour to spend at the gym or anything like that.