Red Bull will have to decide whether or not to stay with Renault for its 2019 engine supplier by the middle of May.
That's the deadline set by Renault F1 managing director Cyril Abiteboul for an extension on their current partnership.
"We are not going to hang around forever," Abiteboul told Motorsport.com at the Circuit de Barcelona-Catalunya.
"There will be a deadline for Red Bull Racing to define what they want for the future. It's available, it's in the Sporting Regulations."
And sure enough, Appendix 9 of the FIA's F1 Sporting Regulations does indeed specify a May 15 cut-off date for decisions about next year's power unit arrangements.
"By the end of May there needs to be some clarity as to who is supplying which team," Abiteboul continued. "Which supplier is supplying which customer team. As far as we are concerned, that will be the deadline.
"I guess that will be the baseline for any discussion," he added. "And then there are still a number of specific services that they want to have.
"The fact that we have that framework in the regs will not prevent any more bespoke services, or commercial discussion, between our two companies."
Yesterday, Red Bull boss Christian Horner said that it was still possible that his team could stick with Renault.
"All things are open for 2019 onwards," he insisted, adding that Red Bull could "absolutely" continue to use Renault engines next year.
Abiteboul agreed that this was the case - provided the deal was done in time.
"I know what Christian is referring to when he says that he has options," he said on Tuesday.
"He's absolutely right. Like him I read contracts, and I know the obligation that we have towards the sport.
"[But] there is one thing that is clear, and that is planning."
Red Bull is also watching closely to how well Toro Rosso's new venture with Honda fares in 2018.
If the senior team did go all-in with the Japanese manufacturer, it would leave Renault with just McLaren as their sole customer team in 2019. But Abiteboul was unconcerned about the financial implications of such an outcome.
"We have always said that being an engine supplier is a very bad business," he said.