Getting the hourly average of a time series dataset

[Raskou07]

Hello guys, I have a large dataframe of 10000 rows and 2 columns .The first column is the dates(years,months,days,hours,minutes) as index. My dates column doesnt have a stable frequency. I am trying to get the average value of 2nd column of every 1 hour .
Any ideas on how can I iterate this problem for the whole time series?
My df looks like this and I want to get the average value from 20:00 to 21:00 and so on.

time value
2019-03-21 20:03:30.351000 22.6
2019-03-21 20:33:30.392000 22.7
2019-03-21 20:38:30.428000 22.6
2019-03-21 20:43:30.363000 22.7
2019-03-21 21:13:30.382000 22.6
2019-03-21 22:33:34.762000 22.5
2019-03-21 22:38:34.696000 22.6