It’s smart to book that tier 2 at 10:15 rather than 10:00. Although, if it were me, I might move that 10:15 a little later. Maybe 10:30 or so. The extra 15 minutes may not sound like much, but if the earliest you can find is, for example, a 9:20 tier 2 after tapping in for your SDD it wouldn’t work because that 10:15 would be blocking it.
ETA: I just checked current FP availability for some of the various shows in HS. Because they are shows, and not rides, the available FP times are spread a bit more than usual. You wouldn't be offered FP times every 5 minutes like many of the rides in other parks.
In using your example above, if you prebook a tier 2 at 10:15, your ONLY option to book another tier 2 after tapping in for SDD (and at a time that preceded the prebooked 10:15 tier 2) would be Voyage of the Little Mermaid at 9:10. The next opportunity to book an early FP would be Disney Junior Dance party at 9:20 as it seems this is the earliest available FP time for DJDanceParty. (I checked multiple dates between tomorrow and mid August and 9:20 was the earliest each time.) I would definitely book that tier 2 burner for no earlier than 10:30. And the Little Mermaid/Disney Jr. Dance Party is a great combo, geographically speaking, for tapping out tier 2’s after exiting Toy Story Land. I should mention that Star Tours does technically offer FPs every 5 minutes beginning at 9:00 am, but I omitted this ride from my considerations because I feel its FP availability will be verify limited after August 29th as it will probably become the most desirable tier 2.
Also, I think ToT FP will be easier to get same-day after the new tiering structure goes into effect.