I'm of ian's generation, and yes, Sunday night as bath night was a general thing. Fitted in well as the only thing on the telly was Songs of Praise. The immersion heater was switched on specially - "Sink" setting, so we got 15 cm or so of water in the bath, no chance of topping up - and shared, at the same time when small, one after the other when bigger.
And before anyone (young) asks, yes, everyone in those days did stink by the end of the week. But as everyone stank, you didn't really notice. Plus the stink of cigarette smoke on everyone and everywhere masked it.