Slippery, supple and sinuous, Hungarian director Lili Horvát’s deliciously reworked psychological noir is a spiral staircase, polished to a glossy shine, down which unreliable motivations, self-delusions and romantic obsessions tumble in gorgeous 35mm. Pivoting on a terrifically self-possessed performance from lead Natasa Stork — in her debut screen performance — “Preparations to Be Together for an Unknown Period of Time” eventually even earns the unwieldiness of its title, as symbolic of the kind of hesitance and second-guessing that is part of the delirium of potentially unreciprocated love. Sometimes the greatest romance is in the waiting; often, it is all in the mind.