Puerto Madero is totally safe day or night. You won't have any problems at all. It's easily the safest part of Buenos Aires due to the all the police there. Thieves don't like to steal things in Puerto Madero because there are limited ways to exit and most of those exits have police at the end of them vs. other areas and parts of the city where there are an unlimited routes to escape.
No need to worry about Puerto Madero at all.
sergio, NO even if there were figures released, they certainly wouldn't be accurate. So I've had hundreds of employees in Buenos Aires and inevitably many of them have experienced crime (mostly cellphones stolen). Not one reported it to the police because they know nothing can be done. The vast majority of people that experience crime (especially locals) don't report it to the police so the numbers would be severely artificially under reported.