While main rivals Red Bull, McLaren, Ferrari and Lotus will all head to Jerez on February 7 with their new cars, Mercedes have opted to spend more time developing their own chassis.
They will instead debut it two weeks later at the second test in Barcelona.
The decision was initially announced at the start of last month and Haug insists it is the right move for Mercedes, even though it leaves them with only eight days of running before the season-opener in Melbourne.
"If you have half-a-year's timeframe to develop a car, then 10 days can be crucial," the vice-president of Mercedes-Benz motorsport explained to Autosport.
"That was our decision. We want to test the proper car, finalised in each and every detail. That's why we need development time.
"It's important to point out that it was a conscious decision. I know that all of the other teams will be there with their car [at Jerez] but this is not unusual.
"Other teams that have been in a catch-up process have decided to go run first at the second test, so this is not a new event.
"We fully appreciate that the other teams have different plans and are ready at the first test. But we are not delayed, we are just following our process, and then we will see what the outcome will be."
Mercedes will, however, still be present at Jerez with last year's W02 chassis, as they seek to understand Pirelli's new range of tyres that were launched earlier this week.
"We will have a couple of parts to learn from at the first test," Haug added. "We can use the new generation of tyres, which is a good way to draw a baseline because you have the data with the old tyres to compare it to.
"We need to learn more about the behaviour of the tyres on our car."