248 days. This reminded me of something I came across in the late 1990s. A particular piece of networking equipment that we had deployed on various customer sites died periodically. From memory it was not 248 days, but memory plays tricks.
The problem occurred at 2^31 hundredths of a second after power up. Well guess what?
2^31 hundredths of a second is indeed 248 days. The time was stored in a 32 bit signed integer, one bit used for the sign and the other 31 bits for the value. After about 248 days there is a risk of an arithmetic overflow and unpredictable software behaviour.
Looks like pretty poor testing for an aviation product.