What should I do when curled up leaf tips?

Opinions on 24hr light schedules aside(I've ran plenty of plants at 24hr for veg with no ill effects), I only have a few small critiques. 1. Your plants look fine, RELAX. Cannabis is a hearty plant and is more often killed from "overloving" them than anything. 2. While I'm not a 24hr naysayers, these plants are hardly into veg growth, they're still establishing a root system and are mostly running on automatic processes. I like to shade my seedlings a little bit. Don't know how "scientific" it is but the thought process is that it helps promote root growth. I know if I have any runty plants a little shade seems to help early on. 3. Be cautious overwatering when starting little seeds in big plants. It's harder maintaining proper moisture levels near the small root system in a big pot. You're often either too wet or too dry. Maybe consider small dose handwatering until they really take off, not on the mainstrem but run a circle a couple inches around it.

Thank you @Organoman ! I'll go for 20/4 since my light is not able to achieve optimal DLI under 24h.

Organomans answer is spot on.