Genie+ Lightning Lanes open up at 7am for everyone, regardless of whether or not you're staying on-property, so you're on an even playing field. Slinky Dog Dash seems to always go fairly quickly after G+ opens up, usually running out not long after 7am, so if you're headed to DHS and want to get a LL for SDD, I'd be on at 7am, and go for that immediately.
The Individual Lightning Lanes are a different story, though. For ILLs, on-property is available at 7am, but off-property doesn't start until park open, so you're at a disadvantage there. I can't speak from experience yet (our trip isn't for a few more months), but most of the reports I've seen so far say that Rise of the Resistance is impossible to get for off-property guests because they're all gone within a few minutes after 7am, long before ILLs open up for off-property guests. That seems to be the only one though, and I haven't read anything about off-property guests not being able to get the other ILLs. I would say try to get the ILLs you want right at park open time to give you the best choice of time slots, but be prepared that RotR likely won't be an option (never hurts to at least check and see, though).
Hopefully others who've experienced things for themselves will give you some useful feedback.
Good luck, and enjoy the trip.