Could be as soon as now, or any amount of time. One of the main things to look for is a fat belly on the female. If she is not already engorged with eggs then it's will take her some time for her to actually create the eggs.
Not a Convict but look how her, the orange one, has a plump looking belly.
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Also a sigh a female is ready to breed is the fact that her breeding tube is down.
Again not a Convict, but it's the same in all fish. Here a female has her tube down ready for egg laying.
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