McLaren racing director Eric Boullier says the Woking-based outfit needs to know the identity of its 2018 engine partner by September.
After a fruitless three years together, McLaren and Honda are weighing their options for next season.
Recent improvements however, as demonstrated by the team's double points-scoring finish in Hungary, may extend the troubled association, especially as both Ferrari and Mercedes have apparently declined to cater to McLaren's power unit needs.
"Technically you could change an engine in 12 weeks," said Boullier in Hungary.
"You can change it anytime before the season up to three months before. If you want to do a base design around an engine, it's September."
The approximate September deadline is also the term sought by Fernando Alonso in order to decide his fate for next season.
Honda has expressed its desire to continue its partnership with McLaren, while also pondering the opportunity to perhaps supply a second team despite its botched agreement with Sauber.
"There is no doubt we would like to stick with McLaren, I think they are getting better performance,"said Honda F1 boss Yusuke Hasegawa who also took encouragement from McLaren's performance in Hungary.
"Today’s result is the sum of a lot of hard work and daily efforts made by the team members, and I want to thank them all for this," he added.
"Although we are now able to head into the summer break with good momentum, we are not satisfied with the overall results of the first half of the season.
"We will continue to push our development for improvement, and hope to have a good start of the second half in Spa- Francorchamps."