I can’t speak to Android as a whole, but here’s how often Samsung Face Unlock will require you to re-auth with your phone’s passcode:

• after 4 hours of not using the phone
• after restarting
• at least once every 24 hours

iPhones do something similar, but it’s after 48 hours of non-use (instead of 4) and at least weekly instead of daily. Having to enter your password daily should help most people keep it memorized pretty well, but weekly - maybe not. So you definitely have a good point there.

One thing that can make it easier to remember - and just as secure - is to use a longer pass phrase instead of random characters.

If you using the diceware approach (“correct horse battery staple”), then 5 words has 32 times / 5 bits more entropy than a 10 character mixed-case alphanumeric password (64 vs 59 bits of entropy) (4 word passphrases aren’t random enough to be recommended - they have fewer bits of entropy (51) than even 9 character mixed-case alphanumeric passwords (53), though notably 10 same-case alphanumeric characters also have only 51 bits of entropy).

The EFF has a word list that’s been improved for usability. They also have a short list, comprised of words with at most 5 characters each, where you roll 4 dice instead of 5. With 6 words from that list you get 62 bits of entropy, which is good enough to be able to recommend.