first off, IANAL so be aware. That said...
"Safely" is a relative term. I mean, the main thing a registered trademark protects against is someone scooping up your game's name, and even then you're only "protected" in the sense that you could win a lawsuit; someone could still try to steal your game's name, and then you'd have to sue them.
That's not super likely to happen as long as you've done your due diligence to make sure nobody else is already using that name. For example you can lookup existing trademarks here. But whether "not super likely" is safe enough for you is, well, relative. I mean, it certainly does happen occasionally.
Either way I would apply for a trademark right away. That's whether or not you release the game before the registration process is finished. The name isn't really valuable yet, but could become so if your game is successful, so you'll want a registered trademark by then.
Also, this related question has more information you should read.