It's grammatically correct, but 'May I' is not natural in this context. It's excessively polite. As well, 'May I' is more used when someone has substantial control/power over you and you are seeking their permission for something. A good example is a student in a classroom. They cannot leave the room unless the teacher grants them permission. The student would say, "May I leave the classroom ? I would reword the sentences as: Can you tell me the estimated time when you may come to a decision?” Can you tell me the estimated time you can move forward with this project ?

“Hello, may I know when the estimated time for you to make a decision?" “May I know the estimated time if you would like to go forward with this project?”