I would pull this out into a function which is called, so as not to duplicate between a NAMEII and NAMEIII and possibly in future used by a NAME trajectory.

i.e.

```Python
def _determine_bounds(time_bla):
    for av_or_int in time_bla:
        method = 'mean'
    ....

def load_NAMEIII_field(filename):
    ....
    cell_methods = _determine_bounds(column_headings['Time Av or Int'])
    ....

def load_NAMEII_field(filename):
    ....
    cell_methods = _determine_bounds(column_headings['Time Av or Int'])
    ....
```