It won't matter...and it won't be seen by the public unless you become a rainmaker (i.e. a paid member).  As a Rainer, only members of Active Rain will see it...and there are not that many that are here...and who are non realtors.

If you were a paid member, I say as soon as possible for more google juice.  Then, share it on social media and then reshare on Thurs or Fri.

BTW, looks like you are fairly close to me as I live in Westchester.  Welcome to Active Rain.

As soon as it is scheduled.

I would suggest doing it several times during the week.

I agree with Roy Kelley .  do several times with a change in some content.

Liana I'd blog as often as possible on different platforms.

Nothing stops you from blogging about an open house more than one time. I would post a blog several days in advance and then post another one the day before your open house. Make some changes in the content so both will be original material. 

Congratulations on the new listing! Tuesday or Wednesday gets you the most sights, but you should repost it on Friday or Saturday morning again.

Good morning Liana. It usually takes us a week of preparation before any open house, so crucial to start now.

Make it a great week!

I would say first of the week and then again toward the end of the week. Make sure you are putting it on networks taht the public can see.

Every single day!

How about the Monday before and then use social media daily up to and including the day of the open house.

I like to do it a week ahead then daily Wed. thru Sunday

sundays are too early... nobody is looking on monday.. i wud start tues... then a follow up thur and fri evening for a sat open

I agree with all the answers here but think that Wednesday is a good day to post the open house for Sunday.