I heard their comment too (it was today) but I call it BS since there's NO evidence that Delpo is a serial time violator.
He bounces the ball like what, three times on average? That means Delpo actually has time to serve multiples of times in the same amount it takes Nadal/Djoker/etc to serve once
Uhm, sorry, but Del Potro does take his sweet time quite often.
It's not merely the ball-bouncing (which he doesn't), it's his very slow pace when walking back to the baseline to serve, when he makes a challenge, etc.
Don't get me wrong - I LIKE the guy - but rules should be enforced.