It's almost certainly normal for this amplifier. I own Lux and Parasound
amplifiers that behave the same way.

It takes several seconds for the amplifier's voltages to stabilize at
turn-on. The protection circuit leaves the speakers disconnected during this
period. It then checks to see whether there's a DC offset at the output (and
possibly at other points). If there is not, the speakers are connected.

Be grateful that the amp and the protection circuit are working correctly.