You can cast them to ints, and then sort.
In [16]: idx = df.columns
In [17]: df.columns = idx.astype(int)
In [18]: idx.order()
Out[18]: Int64Index([1, 5, 10, 30, 60, 120, 300, 600, 1800, 3600], dtype='int64')
You'll need to set the dataframe's columns to the int version. Then call df = df[idx.order()]
.