Assuming that, nowadays, BTC's hodl could be as long as 5 or even 10 years from now.
How long is a long time hodl in alt-coins?
For example, if I'm looking to hodl ARK/STRAT/XMR, what is the right time-frame? is it just for a few months to a 1 year, or can I leave them for 5 years with the hope of weathering the storms and coming out strong?
And besides, do these kind of coins have a 5-10 year lifespan?
from a couple of hours to a week tops.
you can take a quick look at some of the history of the altcoins to see what i am talking about. and then compare it with bitcoin history.
in bitcoin apart from the Mt Gox period (the infamous 2013 pump to $1200 in 1 month) you can only see rise in long term with lots of fluctuation but in the end it is rise.
now looking at altcoins specially smaller ones such as ARK and START you can only see fast and big rises in a short period of time (like in a couple of hours) and they usually last less than 2 days and it is down the hill from there.
some coins have some usefulness so they stick around after the dump but most of them die.