iPhone or iPad, already in Safari: Tap Share (the square with the up arrow), then Add to Home Screen. Turn on Open as Web App if shown, then tap Add.
Opened inside another app? Look in its Share or ⋯ menu for Open in Safari or Open in browser. If you don’t see that option, tap Copy app link below, open Safari on this same phone, paste the link into the address bar and tap Go. Then use Share → Add to Home Screen.
Android: Open Crumb in Chrome, then choose Install app or Add to Home Screen from its ⋮ menu if available.
Settings and active timers stay in the browser or installed app where you started them. Moving to another browser may start a separate session.
Timers recover elapsed time when you return. Sound requires the app to remain open and active; use your phone alarm for locked-screen reminders.