How long will a Chapter 12 discharge take? Since my ETS is July 17, 2020, will they allow me to ETS?

Chapter 14-12 permits discharges for five types of misconduct: (a) minor
disciplinary infractions; (b) pattern of misconduct; (c) commission of a serious offense; (d) abuse
of illegal drugs; and (e) civil conviction.
If your CofC has decided the effort to administratively discharge you under Chap 14-12 is the correct action based on your misconduct, it is reasonable to assume they will do so in a time line remaining you prior to ETS

EDIT of note, the Op posted Chap 12, that is non congruent with his post verbiage hence my response of chapter 14-12

If your unit has ignited (and I mean Ignited) a Chapter 12 then they know your ETS date and they will proceed on the expected time line. It is more likely you will receive a General Discharge if you receive UCMJ action on the causes of the Chapter. Your Jag can answer these questions better because they can access all the documentation and the commanders intent.

Are you sure they initated a Chapter 12, because Chapter 12 covers retirement for length of service. If they have initiated a Chapter 13 or 14 knowing that it your intent to ETS, your Commander probably intends to seek a General discharge. Some provisions of Chapter 13 and 14 require initiation of the discharge.