It's not uncommon to have a fast core and then an API that alpha / research teams feed signals into

if you are someone like HRT I presume the bulk of their money comes at very short holding periods so you have e.g. fast signals that work short term and then mid frequency alpha signals that spit out a forecast over a few timeframes i.e. it might not be that they buy (aggressively) really quickly but rather than someone sells to them and then they hold onto the position for longer than they would if they have no opinions.

Similarly this shapes where you post your orders e.g. if you really want it then you want to be top of the book