Complex sentence: Wilkie 1924, pp.145--146 At 18:30 the RHA withdrew, then confusingly the regiment was ordered to remain where they were, until the yeomanry to their left had moved back.
Split into simpler sentences: Wilkie 1924, pp.145--146 At 18:30 the Royal Horse Artillery withdrew. Then, confusingly, the regiment was ordered to remain where they were, until the yeomanry to their left had moved back.