The FAQ states https://web.three.com.hk/esim/faq_en.pdf
"Customer can enjoy 10-Day roaming day pass in designated destinations within 90 days after eSIM activation.
...
10-Day pass can be consumed continuously or on a daily basis separately. Customer can enjoy the Roaming Data Day Pass in various destinations while travel on the same day.  Roaming Data Day Pass will be terminated on the respective end day of Hong Kong time 23:59 automatically and there is no pro-rata calculation even the Pass is effective in the middle of the day."

FAQ is also in small text at the bottom of this page: https://www.three.com.hk/eSIMMall/ch...x.jsp?lang=eng. Unlimited Data is higher speed data 500MB/day as noted by sixpaq and is stated in daily fair usage policy at the bottom of Terms & Conditions https://web.three.com.hk/esim/tnc.pdf. After that it gets throttled to min 128k.

Yes, I activated a 3HK esim and haven't used esim mobile data yet. I confirmed it latched to AT&T on roaming for several hours without enabling mobile data on esim. I didn't need it on my last trip and the 10-day pass will still be valid for the duration for my next trip. If I have the option, I prefer to activate and test top up reasonably ahead of time as top up/reload can take a while on different carriers (local acct only, topup resellers down, not available outside country, etc). Chalk it up to lessons learned with buying plenty of local and roaming sims and keeping some of them active.