def parsetime(v):
    return np.datetime64(datetime.datetime.strptime(v, '%d/%m/%Y %H:%M:%S.%f'))
content = np.loadtxt(filename, dtype={'names': ('timestamp', 'tick', 'ch',
    'NodeI', 'Base'), 'formats': ('datetime64[us]', 'i4', 'i4', 'i4', 'i4')
    }, delimiter=',', skiprows=27, converters={(0): parsetime})
Read a custom formatted datetime with numpy