Don't worry about resting too often in Baldur's Gate 3—except when a quest tells you otherwise
You don't have to rush to beat the main quest, but some sidequests do have time restrictions.
When I first started playing Baldur's Gate 3, I figured I was on a time crunch: "I've got a tadpole in my head! I can't dawdle!" I wasn't sure if this plot-important parasitization would progress to a critical state if I took too many long rests—the health and spell-restoring function of Baldur's Gate 3.
Thankfully, this isn't the original Fallout—you're pretty free to take long rests whenever you see fit, even when some plot events seem like they might progress if you take too long. Sleeping can trigger scenes related to the main quest, but what we've found is that the quests themselves rarely advance without your input, unlike the notoriously time-limited companion quests of Baldur's Gate 2.
There are exceptions: Sometimes characters will tell you that there's a time limit on their offer. If they refer to "the next day," that means after your next long rest. Those are the main things you need to know, but if you want to understand more about time progression in Baldur's Gate 3, read on—some Act 1 spoilers follow.
I was feeling the pressure of Kagha's Ritual of Thorns at the Emerald Grove, but it really only comes to a head as you advance the plot of the Grove vs the Goblins. One thing I'm less sure of is how the slightly hidden and tangentially related quest, Investigate Kagha (one of our five things not to miss in the opening hours of Baldur's Gate 3) is affected by advancing the main story of the Grove—there's a lot of different variables at play, and I've yet to see what happens if you bring Halsin back without first investigating Kagha.
If you agree to Drow Paladin Minthara's assault on the Grove, she says the attack will begin the next day and she means it—a long rest will trigger the battle sequence, and if you want to side with the Grove, you'll no longer be able to sneakily take out the Goblin leaders in their camp and will instead have to betray them at the assault.
But overall, you can take your time with Baldur's Gate 3 and rest up when you need to—it's a challenging game, and for the most part you'll want to be at peak strength when you stumble across a tricky fight. You'll just want to pay attention to what quest givers tell you about the timing of their tasks, and plan accordingly.