Enable the option to use cron strings when configuring the interval of the Timer trigger in Embedded workflows. This capability is already available in other workflow types, and the goal is to extend the same functionality to Embedded workflows for consistency and improved flexibility.
I will file this as a feature request. Note, however, that it will be up to the device to provide the actual current time in milliseconds since Epoch for a cron string to even be effective. In some cases the hardware may only be able to provide the number of milliseconds since it booted up, which would leave a cron string unusable.