Now is not a good time / The timing isn't right
Literally 'the oven isn't ready for buns'. Means this is not the right moment to ask for something or raise a topic, as the person or situation isn't receptive.
Don't ask him for a favour today, now is not a good time.
—Should I tell her now? —The timing isn't right.
After the meeting, it really wasn't a good time.