When Jim and I were selecting which combination of HD wallet structures to support we noted the following:
*
BIP39 is a good standard list to select from that mandates words that
do not look similar to each other, a certain spelling (no English US/UK
confusion) and possible foreign language variants provided by experts
later
* BIP32 (m/0h/0/0) and BIP44 (m/44h/0h/0h/0/0) allow for maximum compatibility with other wallets
*
including a date in the "wallet words" themselves is open to spoofing
since the generator cannot be sure the date is correct (local time
drift, provided externally by untrusted third party etc)
* a timestamp as optional external metadata is useful to reduce sync times in SPV
*
our experience verified that users will very often enter a timestamp
incorrectly (locale, fat fingers, bad memory etc) so we opted for
"number of days elapsed since Bitcoin genesis block with a modulo 97
checksum appended" (e.g. 1850/07) to mitigate this
* if a user
has no timestamp then blank is the only alternative (no guessing) which
is interpreted as "earliest possible BIP32 date"
