Python, round DOWN time to the nearest 15mins clock mark

Question

how am i able to round down time to the nearest 15mins clock mark. the code below rounds to the nearest 15mins clock mark, i.e if time is 5:08 to becomes 5:15. however i would like to make this round down not up and become 5:00 please help

here is my code

fajr_jamaat = ceil(fajr_jamaat_date).strftime('%H:%M:%S')

and the function is

def ceil(dt):
    if dt.minute % 15 or dt.second:
        return dt + timedelta(minutes = 15 - dt.minute % 15, seconds = -(dt.second % 60))
    else:
        return dt

Answer 1

this should work.

import datetime

def ceil(dt):
    minut = int(dt.strftime('%M'))*60
    secon = int(dt.strftime('%S'))
    h = int(dt.strftime('%H'))
    tot = minut + secon
    #print(tot)
    nearest = round(tot/900)*900
    #print('time is %d:%d'%(tot/60, tot%60), 'nearest fifteen mark is %d:%d'%(nearest/60, nearest%60))
    if nearest/60 == 60 and h < 23:
        nr_15_mark = dt.replace(hour=h+1, minute=0, second=0)
    elif nearest/60 == 60 and h == 23:
        #wrapping the hour back to 0 
        nr_15_mark = dt.replace(hour=0, minute=0, second=0)
    else:
        nr_15_mark = dt.replace(minute=int(nearest/60), second=nearest%60)
    return nr_15_mark

#fajr_jamaat_date = datetime.datetime(2017,1,1,23,58,0)
fajr_jamaat = ceil(fajr_jamaat_date).strftime('%H:%M:%S')
#print(fajr_jamaat)

Please note that as we are considering only hours, minutes and seconds, i'm ignoring the date addition when we are finding the nearest mark when the time of fajr_jamaat_date exceeds 23:47:30.