In the first part of her trip, Diana will cover 2 hours * 3 mph = <<2*3=6>>6 miles.
In the second part of her trip, Diana will need to cover an additional 10 miles - 6 miles = <<10-6=4>>4 miles.
To cover 4 miles * 1 mph = will take Diana <<4*1=4>>4 hours.
Total biking time to get home for Diana will be 2 hours + 4 hours = <<2+4=6>>6 hours.
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