"when about" is not correct or usable in written English.
It is not an idiom or phrase, so it does not have any meaning.
Macroscopic failure of the tensile specimen occurs when about 25% of the particles are fractured.
The CO conversion reaches a maximum, when about 20 wt% Mo2C is loaded on active carbon.
Both randomization tests and the algorithm of Dong become unreliable when about 50% of the examined factors are significant.
Jennifer Negron was the city's first homicide of 1992, when about 2,000 people were murdered.
The audience for "Idol" finales peaked in 2006, when about 36 million people tuned in.
The interlayer space of graphite oxide was saturated when about 11 mmol/g of n-hexadecylamine was included in it.
It is a huge reduction from 2010, when about 63% of pension applications were approved.
Americans might vote in presidential elections, when about 60percentt of eligible Americans vote.
These conditions caused the now infamous 1952 London smog, when about 12,000 people died.
It is updated every Wednesday morning, when about 1,000 new pieces are added.
She became visibly irritated, however, when about 20 students tried to disrupt her speech.
