gausus wrote:If I want to use it in a assault phase do I activate it at the end of my shooting phase, before I run the assault?
That's correct. This means you might activate the standard, then fail to make the charge distance.
gausus wrote:And If I would like to benefit from the standard when I'll get assaulted? When should I activate it then?
Any time before the assault phase. Once again, by the assault phase, it's too late - if you activate it during an assault phase, it won't take effect until the next one. This means that your opponent might decide not to charge the unit that activated its standard.