You may use either. Strictly speaking, your choice should be governed by the context in which you are speaking of your schedule.
If you are speaking about your activity during those two weeks, you should use the past form:
In the last two weeks I didn't have much time: I was at the office for ten or twelve hours a day, including weekends.
In the last two weeks I didn't have much time, so was unable to look up that quotation I promised you.
If on the other hand you are speaking about your current state or intentions, you should use the perfect form:
In the last two weeks I haven't had much time, so I haven't got that quotation for you.
In the last two weeks I haven't had much time, but I expect to be able to address your question soon.
In colloquial use, however, particularly when the fairly recent past is concerned, you are likely to hear either form regardless of context.