I can open https://timechaincalendar.com/en in my phone browser (Duck duck go). It looks like a web page. How to turn in into full screen app?
PWAs as Tools to Benefit Future Development of Nostr
In light of Apple's recent actions against Damus and the broader zap functionality, concerns are growing among the Nostr community and beyond (thank you, nostr:npub1sg6plzptd64u62a878hep2kev88swjh3tw00gjsfl8f237lmu63q0uf63m for highlighting this on the blue bird app).
As the pushback from traditional institutions - including tech companies, governments, and regulatory bodies - is likely to escalate, many are exploring viable alternatives. One of these, as recommended by nostr:npub1cmmswlckn82se7f2jeftl6ll4szlc6zzh8hrjyyfm9vm3t2afr7svqlr6f among others, is shifting towards Progressive Web Apps (PWAs). This strategy could help us break free from the limitations imposed by centralized app store authorities who dictate what can and cannot be incorporated into Nostr clients and other apps interacting with censorship-resistant protocols.
If you're new to the concept of PWAs, check out my brief overview: https://lnshort.it/pwa/
Discussion
Safari provides an option to add a webpage as a shortcut on the home screen. Android should have something similar. 
I used the option "Add to home screen" in duck duck go and it created a shortcut on the home screen, which opens duck duck go with the page. Not a real app!
I tried with Chrome. It has option "Install app", which works as expected! Thank you!!!
Yep, native browsers normally have this option. Chrome on iOS doesn’t for this very reason probably.
Glad it worked.