Is the congregant considered late in relation to the imam if he remains bowing until the imam stands upright, or prostrating until the imam sits, bearing in mind that the imam may not raise his voice with the Tasmi’ (saying “Sami’a Allahu liman hamidah” – Allah hears those who praise Him) until after standing upright or sitting?

The Sunnah is for the congregant to rise from bowing immediately after the Imam rises, without delay. However, if the congregant delays rising from bowing or prostrating after the Imam, and catches up with the Imam in the subsequent pillar before the Imam descends to the pillar after that, this does not invalidate the prayer. This is because it is a delay within a pillar, not a delay by an entire pillar.