The phrase "simultaneously when" is correct and usable in written English.
You can use it to describe two events occurring at the same time. For example, "My head was spinning simultaneously when I experienced a wave of nausea."
His second foul and the blood came simultaneously, when Wall plowed through him in the backcourt.
The trick, analysts said, is persuading both sides to act simultaneously when each wants to see the other move first.
It is literally impossible for a system to satisfy all of these needs simultaneously when they are contradictory.
The free download of the band's album was announced – and happened virtually simultaneously – when U2 performed at the Apple iPhone launch event in Cupertino, California on 9 September.
*The car collision of appetite and discomfort one feels simultaneously when using the internet to seek and consume images or information that may be considered unseemly or inappropriate.
Exercise physiologists say it can be impossible to demonstrate its value because usually too many things change simultaneously when people start to run in groups: the coach, the location, the training regimen.
A few weeks later, the wasp offspring emerge simultaneously when the male flowers mature.
Simultaneously, when determining the infrastructure configuration design, the water flow rates are optimized.
The results suggest that neuroticism and self-esteem should be evaluated simultaneously when analyzing depression disorders.
The in-situ TiC surface composite coating was synthesized with cast-cooper simultaneously when cooled down.
However, MRDs increase damping and stiffness of a system simultaneously, when a magnetic field is applied.
