Here's an example. You'll need to calculate the hour intervals needed:
import math
end_date = system.date.now()
start_date = system.date.addDays(end_date, -1)
difference_in_seconds = system.date.secondsBetween(start_date, end_date)
total_hours = difference_in_seconds / 3600.0
hour_windows = math.ceil(total_hours)
paths = ['histprov:Historian:/prov:default:/tag:Ramp/Ramp0']
aggregates = ['Average']
result = system.historian.queryAggregatedPoints(paths=paths, startTime=start_date, endTime=end_date, aggregates=aggregates, returnSize=hour_windows)
for r in result: print r[0], r[1]