I'll write you guys out the timeline for this. Note: I also went and found a calendar online to make sure my dates and days of the week lined up properly.
11th of September: Harry sleepwalks into the Slytherin quarters for the first time.
21st of September: Slytherin Boys figure out how Harry has been getting in.
22nd of September: Draco alerts Snape to Harry's sleepwalking. Snape talks to Harry before breakfast.
23rd: Harry sleepwalks into the Slytherin quarters again and lays with Theo. Gets deaged by his magic
25th: Harry goes to Grimmauld Place and meets Sirius and Remus again. Sirius has a confrontation with Molly and others.
Late at Night on the 25th: Blaise and Harry bond a bit. Lady Magic brings Regulus Black back to life.
26th: Harry meets Regulus Black. Reglus attempts to babysit his nephew. It doesn't go well after a point. Remus ditches a mission to be a good Moomy. Harry gets ill.
Late the 26th/early the 27th: Sirius and Remus take care of Harry throughout the night and during the day of the 27th.
27th: Blaise and Theo have a confrontation with Umbridge in the hall.
28th: Minister Fudge pays a visit to Snape to inquire about the baby that had been with Blaise and Theo.
Later on the 28th: Snape goes to Gringotts to fully claim his lordship and finds out several interesting things.
29th: Harry spends a bit of bonding time with Regulus because Sirius injured himself falling down the stairs and into a wall. Kreacher has a good heart on this day.
30th of September: Draco, Theo, Fred, George and Hermione are gender-swapped by Ronald and Ginerva Weasley. The Twins and Granger go shopping with the Slytherin part of Harry's new family.
11th of October: Been a month since Harry regressed. The Slytherins have grown closer to Twins and Granger enough to consider them friends. Neville joins their friend group. Sirius and Regulus have bonding time with each other. Remus makes friends with a new Alpha.

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Slytherin Boys
FanficStrangeness in the Slytherin Dorms. NOT FREAKING DRARRY! I'll be going through and fixing things in old chapters at times. Dumbledore is bad. Umbridge is also bad obviously. Set fifth year and on. Ginny bashing. Hermione is bitchy for awhile and Ron...