Guys here's your solution. The edge clock is accessible by choosing the type of clock to display. Details here: https://www.sammobile.com/2018/06/05/psa-night-clock-moved-always-on-display-settings-oreo-galaxy-s7...
Is not the same.
With Android 7 we can use Edge clock in some hours and the others we can use AOD (in my case, for example, Edge clock between 0.00h and 7.00h and AOD between 7.00h and 23.59h).
With Android 8 we just have a period option, so we use Edge clock or AOD, not both.