You need to give it a good month before they get to full speed in my opinion.
then after a couple of months you get familiar with each other (not in that way!) and your workrate drops off as you drop back to a comfort zone ... just saying
My Story
I started with someone years ago and it was amazing how much we got through some days we would be worked up just after mid-day life was great money was great and we were rocking ...
then we started having a laugh, ribbing each other and sharing private jokes ... same age ... going to each other bbqs ... birthday in the same week ...pub on a friday ... it was like a scripted 'bro-mance' work rate dropped off but we still covered it all by the afternoon ...
then we noticed that a few of the local cheap pubs had specials on food and a pint if ordered before 1 o'clock in the afternoon ... seemed like a great idea ... 18 months later I was no better off than when I was on my own!
Conclusion ... I am a crap motivator of myself and others!