Now that we are in the last stage of preparation (hopefully) I have a question about the summoning.

Would it be ok for a Master to summon their Servant in advance to the HGW, like any of the actually accomplished Magi of SN and Zero did?

I'm asking that because it feels counterproductive to summon a Caster at the last minute. If Emilia can do it beforehand, she'll certainly do so, especially considering how deliberated her choice of Servant was.