The triple DTM champion believes that the victory achieved by Laurens Vanthoor, Kevin Estre and Andre Lotterer for Porsche Penske Motorsport in the Qatar 1812km season-opener gives BMW "hope" in the first year of its WEC programme with the M Hybrid V8 run by WRT.
But he stressed that following a best result of 10th at the Losail International Circuit, promoted into the points by Cadillac's disqualification, BMW still has work to do.
Asked by Autosport for his views on the impact Porsche's victory has had on the BMW camp, Rast said: "It definitely gives hope because you can see that the LMDh car actually can fight for overall victory, we are the same car category more or less, so the potential is there.
"But probably we need a bit more time.
"Our test programme in the winter or last year for this season was a bit compromised due to a lot of weather. I’m not saying that this is the reason, but we were not very lucky with the weather conditions and didn’t do a lot of dry running.
"Every test we get now in dry conditions helps a lot to just make another step.
"Even though it’s just for driver comfort or more consistency in the car, that helps already. We just need more time and more testing to get on that level."
BMW Motorsport boss Andreas Roos also urged caution on the Bavarian marque's first WEC programme since its M8 GTE contested the GTE Pro class in the 2018-19 'superseason' with the MTEK squad.
The M Hybrid V8 uses the same spec rear axle hybrid system as Porsche's 963, and was raced in the IMSA SportsCar Championship last year by the Rahal Letterman Lanigan Racing squad, but Roos pointed to the several operational differences between IMSA and the WEC to justify a need "to be realistic".
"We have all the ingredients that we need," he said.
"But whether we can extract everything from those ingredients, that is the question. We still have a lot of work to do, we are not where we want to be.
"Qatar for sure didn’t go as everyone wanted, but it was our first race in the championship. It was also the first time WRT was operating the cars under race conditions.
"We learned a lot, but we still have to improve a lot."
WRT boss Vincent Vosse expressed optimism that the team is "going in the right direction" following its graduation as champion of the LMP2 category that was dropped from the championship this year.
"If you came to the box during the race at Qatar, it was a normal race, nothing hectic," he told Autosport.
"The drivers weren’t complaining about the car, it was not like we were having big issues. I have to say it is part of the process.
"I remember one of those teams that I have a lot of respect for, Penske is a good example, the first three or four races [in 2023], they struggled.
"We were saying that is not what we were expecting from Porsche and Penske. That proves it takes time."
