Just spend the time you can. When napping, dinner and playing perhaps you could do it together with your helper. Though it is emotionally and physically tired, atleast you have that ample of time spend with your first born. Once you have your second born, attention divert a little and first born could feel left out. You don't have to do it long, atleast those period that Ive mentioned and the time you have lots of energy and you're okay that would be perfect.