Misaligned dates for cross-day calculations

I have the following function that for a provided date and a pair of lat/long variables is supposed to return the the list of 3 timestamps in UTC

one in the afternoon on that day
one in the late evening on that day
and next one shortly before sunrise next day.

Unfortunately, likely because the calculations jump from one day to another, the results are totally off. Where I got this wrong? Is there a better approach to this?

import datetime as dt
from suntime import Sun

def key_timestamps(date, latitude, longitude):  
    date = dt.datetime.strptime(date, "%Y-%m-%d")
    
    sun = Sun(latitude, longitude)
    
    sunrise = sun.get_sunrise_time(date)
    sunset = sun.get_sunset_time(date)
    
    next_day = date + dt.timedelta(days=1)
    sunrise_next_day = sun.get_sunrise_time(next_day)
    
    solar_noon = sunrise + (sunset - sunrise) / 2
    peak_heating = solar_noon + dt.timedelta(hours=2, minutes=30)
    evening_release = sunset + dt.timedelta(hours=3)
    morning_minimum = sunrise_next_day - dt.timedelta(hours=1)
    
    return [
          int(peak_heating.timestamp()), 
          int(evening_release.timestamp()),
          int(morning_minimum.timestamp())
          ] 

singapore_results = key_timestamps("2022-05-29", 1.3521, 103.8198)
print(singapore_results)

Output is [1653809526, 1653746868, 1653947784] which translates to:

Sunday, May 29, 2022 7:32:06 AM - probably correct
Saturday, May 28, 2022 2:07:48 PM - should be a few hours later than #1 so totally wrong
Monday, May 30, 2022 9:56:24 PM - also wrong

Another example:

la_results = key_timestamps("2022-05-29", 34.0549, 118.2426)

Output:

[1653806070, 1653747048, 1653940656] which translates to:

Sunday, May 29, 2022 6:34:30 AM - wrong
Saturday, May 28, 2022 2:10:48 PM - wrong
Monday, May 30, 2022 7:57:36 PM - wrong

Solution

Sun.get_sunset_time() appears to return the sunset time from the previous day (even if you set the time component to 23:59:59) so to get today's sunset time you need to add 1 day.
You also may need to pass in a time-zone aware datetime and then use Sun.get_sunrise_time(date, tzinfo) (and for sunset) to ensure that the output has the correct time zone.

from datetime import datetime, time, timedelta
from zoneinfo import ZoneInfo
from suntime import Sun

def key_timestamps(date, latitude, longitude):  
    sun = Sun(latitude, longitude)
    
    sunrise = sun.get_sunrise_time(date, date.tzinfo)
    sunset = sun.get_sunset_time(date + timedelta(days=1), date.tzinfo)
    sunrise_next_day = sun.get_sunrise_time(date + timedelta(days=1), date.tzinfo)
    
    peak_heating = sunrise + (sunset - sunrise)/2 + timedelta(hours=2, minutes=30)
    evening_release = sunset + timedelta(hours=3)
    morning_minimum = sunrise_next_day - timedelta(hours=1)
    
    return [peak_heating, evening_release, morning_minimum] 

singapore_results = key_timestamps(
    datetime(2022, 5, 29, 0, 0, 0, tzinfo=ZoneInfo("Asia/Singapore")),
    1.3521,
    103.8198,
)
print(singapore_results)
print([int(t.timestamp()) for t in singapore_results])

Outputs:

[ datetime.datetime(2022, 5, 29, 15, 32, 6, tzinfo=zoneinfo.ZoneInfo(key='Asia/Singapore')),
  datetime.datetime(2022, 5, 29, 22, 7, 48, tzinfo=zoneinfo.ZoneInfo(key='Asia/Singapore')),
  datetime.datetime(2022, 5, 30, 5, 56, 24, tzinfo=zoneinfo.ZoneInfo(key='Asia/Singapore'))]
[1653809526, 1653833268, 1653861384]