Hi @Gerard2 :
Could you tell me:
What time zone are you in?
I assume you use UCT time then please try this flow:

Reference Expression:
if(greater(int(formatDateTime(utcNow(),'HH')),18),'Good evening',if(greater(int(formatDateTime(utcNow(),'HH')),11),'Good Afternoon','Good Morning'))
If you are in another time zone, just add the offset value. I assume you are in the UCT+8 time zone
The expression should be:
if(greater(int(formatDateTime(addHours(utcNow(),8),'HH')),18),'Good evening',if(greater(int(formatDateTime(addHours(utcNow(),8),'HH')),11),'Good Afternoon','Good Morning'))
Best Regards,
Bof