Can I report early if my orders state "report date: NLT date "?

You can report up to 30 days early, but your DA31 must cover you to your report date.
If you're coming from OCONUS, there are DEROS rules that apply to when you can leave as well

So, NLT meaning "not later than"... Whenever your departing command wants to release you, you could report in to your new unit the next day if you wanted. If this is currently not the case in the Army then the Army needs to stop using NLT on it's orders.

When I got to JBLM and tried to sign in 2 days before my report date, reception said I couldn't because nowhere on my orders did it say "early reporting is authorized." I got to JBLM like 3 weeks early because there was an opening for housing and then daycare as well and got that set up. I don't know if that was just a JBLM reception thing. I had to come back two days later (a Saturday) to sign in. I had taken 30 days of leave - like half of it at home and then half getting there early.