With 26.4 beta 2 announce the time is no longer using the voice I have selected. I am using Australian English Siri 2, however it will speak using American English Samantha. I also have the system voice set the Australian English Siri 2 which is never honored. In fact, with that setting, Speak announcement never happens. Speak announcements has been broken since 26.0. There are several other issues with text to speach. Basically, TTS works for the most part if you use the default Samantha voice. Various things break when using other voices.
FB22035712 -- "Announce the time not using selected voice" FB22035743 -- "Speak announcements only works if Samantha voice is selected."
I will note that FB20933185 -- "Siri voices break System voice UI" appears fixed in 26.4 beta 2, in that the UI is no longer broken with Siri voices, but now Siri voices aren't honored.