Exercise-more important for weekly total or daily total?

explainsitall

Hey MFPers,

Is it better to exercise every day for a consistent time or to have an overall total of minutes worked out per week? For example, MFP recommends for me to eat 1,200 Calories a day and work out for at least 30 minutes/burn 188 calories. Let's say I have two or three days where I know I can work out for an hour and a half, but other days when I know I don't have 30 minutes to work out. Is this still as effective, or is it better to spread out over smaller increments?

For the record, I try for at least an hour a day but some days I just can't quite make it.