It's a piece of code that's essentially an expiration date in the kernel for said flashcart device(s). The kernels are just DSTT clone kernels that overall feel clunky, two options to fix the issue, change the date of your system, or use YSMenu. The proper solution would be to buy a better flashcart running a good kernel, example, the R4i Gold 3DS Plus is a very good flashcart to get, it runs Wood R4 and doesn't have time bombs at all.
Sorry for the bump, just had to stress this.