In fa-in, fa is connective and in is the conditional particle. Qaddama is a Form II past verb from q-d-m meaning 'brought forward'; al-ramya is its accusative object.
Qabla and baʿda are temporal expressions ('before' and 'after'). Jāza supplies the resulting permission, while ʿinda Abī Ḥanīfah explicitly attributes the ruling to Abu Hanifah.