If applying Early Decision, will a college look at Senior grades since the application will be due after the first quarter because most colleges ask for the first semester and not the quarter.
You should ask your school if they send in an update for the quarter for ED applications.
But the school will look at them at some point and can rescind admittance so don’t assume you can slack off too much after an ED acceptance 
The school my DS applied to Early Decison said:
Students applying Early Decision (either EDI or EDII) should have their first marking period grades sent directly to our office as soon as they are available.
The general rule is that first marking period grades are sent before ED decisions are made. In addition, the final transcript is sent and every college retains the right to rescind an acceptance if the grades drop dramatically.