6pm to 3am is for the JP/EU servers, since they're also releasing patch 4.57 today. The NA servers have a longer maintenance window due to the datacenter split.

https://na.finalfantasyxiv.com/lodes...ede8c253c9720b

[Date & Time]
Apr. 22, 2019 3:00 a.m. to Apr. 23, 2019 3:00 a.m. (PDT)
* Completion time is subject to change.

[Affected Worlds]
All NA Worlds

[Affected Services]
World Transfer Service (All Worlds)