Operation: Parenting's timeline in the beginning wasn't such a beast to wrangle (mostly because it was supposed to just be one, maybe two one shots), but as the series grew, the need for further worldbuilding and a cohesive timeline became necessary.

Operation: Parenting covers from January 1st, After Colony 199 (when Heero becomes a parent) all the way until April 4th, After Colony 252 (when Heero passes).

If a date is 00.xx then that means there was never a specific day, just a specific month. Likewise if it just lists a season.

THE TRUE & HONEST TIMELINE
last updated 27 September 2023

199
01.01 - there will never be a father who loved his daughter more than i love you [*] - Millie's birth
01.16 - All You Need to Be
01.xx - heal the wounds or crack the shell
12.11 - How Lovely are Thy Branches?
12.25 - Perfectly Imperfect Christmas [**]

[*] replaces "For Everything"
[**] Christmas in this 'verse isn't celebrated on 25 December (due to 12.24 being a day of mourning since that was the day the war ended), it's actually combined with New Year's (01.01). When I wrote this fic, it was specifically as a Christmas fic for Christmas. When I do a rewrite of it I'll redate it appropriately and update the timeline.

202
10.xx to 11.11 - House Hunters Makes House Hunting Look Easy [Moving Transatlantic 01/04]
11.xx - EDM Makes Moving Tolerable After Your Best Friend Steals a Jet [Moving Transatlantic 02/04]

203
01.20 - Let's Get Down to Business to Defeat the Fug [Moving Transatlantic 03/04]
01.27 - I Need to Feel Your Deathless Death [Moving Transatlantic 04/04]
03.25 - School Hunting is Even Worse Than House Hunting
05.02 - Like a BOGO Deal - Aiden and Odin's birth

204
07.xx - The Best Parts of Me
11.08 - outlier [*]

[*] replaces "Full of Surprises"

206
04.23 to 05.06 - sometimes it hurts to feel anything at all - Heero loses his unborn daughter and his left leg

208
06.07 - Kiss Me Under the Stars

210
12.16 - where do we go from here? [(Re)Discovering Family saga]

214
06.10 - The Truth of Myself - Noin's coming out

215
06.03 - Pride at Riverside
06.14 - #HisNameIsOscar

216
07.xx - Hard to Explain, Difficult to Define

217
06.01 - Netflix & Kiss - Aiden's first kiss with Ethan

219
06.04 - He Loves Me Not

220
Autumn - Always Look Towards the Sun [Rhythm Generation: The Measure of a Year]

227
06.02 - Valid - Odin comes out as nonbinary

236
06.11 - A Family Tradition [sequel to Pride at Riverside] - Heero learns he's becoming a great-grandfather

246
06.14 - pleasures of the flesh [Into the Depths saga]

252
04.04 - heavy is the crown

there will never be a father who loved his daughter more than i love you and heavy is the crown are the canonical beginning and ending of this series, respectively. heavy is the crown segues right into the sequel series, Heavy is the Burden.