It’s not quite that - it isn’t a period piece as such … reports are that is set in a different multiverse in which it is modern day but what a modern day would be if the whole 1960’s Tomorrow Land ascetic became a reality in the modern world.
By the end of the movie, the Fantastic Four are said to somehow end up in ‘our’ MCU reality …
So, instead of time travel, she'd need to cross universes...
You think that is somehow less awkward for something that is unlikely to be core to the plot of the movie?