How does Apple's app review work?
My guess is if you put 10 or 30 apps in for review, you might [and probably should] have a hold or slowdown, but for only two apps, I doubt there is any meaningful delay by having more than one app in the queue. 

See the published app submission guide on Apple's developer web site. It also mattes if you are submitting an update as opposed to initial submission of an app for initial review and first sale.