We have read https://developer.shopware.com/docs/guides/plugins/plugins/plugin-fundamentals/add-scheduled-task which described how to define a scheduled tasks which runs every x minutes.
Is it also possible to specific the execution time, for example each midnight or every day a 2 am, like in a crontab?
There is no such possibility in Shopware 6. It is easier to accomplish this with a CLI command and crontab. But if you have to use Shopware's scheduled task then you can trick it by setting the nextExecutionTime to the time you want to execute the task.
For example if today's date is 10.03.2022 and you want to execute the scheduled task every day at 2 am then set the nextExecutionTime to 2022-03-11 00:02:00.000 (use future date) and runInterval to 86400 (24h). This way Shopware will start the task at 2 am and then set the nextExecutionTime to the next day at 2 am (+- couple of minutes from my experience).
I'm not aware of such a feature in Shopware core.
The probably most straightforward way would be to add a "real" cronjob like you mentioned, which triggers a CLI-command.
You can encapsulate the logic of the task in it's own service, so that the scheduled task and cli-command both can just use the service (if you want to keep both).
