How long does it take to pasteurize something at 60C?
According to J.D. Schuman, info that I found in Douglas Baldwin's guide for sous-vide:


  Place egg in a 135°F (57°C) water bath for at least 1 hour and 15 minutes (Schuman et al., 1997).


J. D. Schuman, B. W. Sheldon, J. M. Vandepopuliere, and H. R. Ball, Jr. Immersion heat treatments for inactivation of Salmonella enteritidis with intact eggs. Journal of Applied Microbiology, 83:438–444, 1997.

This is for whole eggs in the shell, so for your custard the time should vary according to the volume (as it will take longer for the temperature to reach the  center).

Here is a time table for Salmonella reduction from The Modernist Cuisine (by Nathan Myrvold):