diff_time
0
12
44
2
2
13
3
208
2
21

for el in df['diff_time']:
    if el > a:
        return b
    else:
        return None

from scipy.optimize import minimize, rosen, rosen_der
duration = [some data]
res = minimize(rosen, x0, method='Nelder-Mead')
res.x