«In» often accompanies a present-form verb, whereas «idha» and «law» frequently appear with past-form verbs. Grammatical form and the intended temporal meaning are not always identical in a conditional construction.
The discussion also relates «in» to jussive conditional usage and «idha» to actual occurrence. Detailed parsing belongs to syntax; the rhetorical question is what expectation the construction communicates.
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Al-Itlaq wa al-Taqyid: Rhetorical Functions of Unrestricted and Qualified Expression
«In» often accompanies a present-form verb, whereas «idha» and «law» frequently appear with past-form verbs. Grammatical form and the intended temporal meaning are not always identical in a conditional construction.
The discussion also relates «in» to jussive conditional usage and «idha» to actual occurrence. Detailed parsing belongs to syntax; the rhetorical question is what expectation the construction communicates.