If you read the technical stuff on the Levemir website, with higher doses, you can get it to last 23.2 hours. With Levemir, the more you take, the longer it will last, but if you do that, you will also have periods where you are running low because you are taking more basal than what you need. I actually take mine 3 times a day – mine lasts for about 7 hours.
I copied the paragraph pertaining to how long it lasts - I have it in a PDF but don't know how to attach that here.
Insulin detemir is a soluble, long-acting basal human insulin analog with a relatively
flat action profile.The mean duration of action of insulin detemir ranged from 5.7 hours
at the lowest dose to 23.2 hours at the highest dose (sampling period 24 hours).
The prolonged action of LEVEMIR® is mediated by the slow systemic absorption of insulin