This article explains the best times on Tumblr, along with Facebook and Twitter, to post information that will be seen by followers and commented on. The article states that the best time to post and receive the max amount of responses for Facebook and Twitter is between 1 p.m. and 3 p.m. Monday through Thursday. This is the best time to post for Facebook and Twitter as the majority of people will see the post because the range of people on Facebook and Twitter is greater than that of Tumblr.
For Tumblr, posts should be made between 7 p.m. and 10 p.m. Monday through Thursday. Tumblr has been researched to contain mostly high school to college students as their members. This is the age range of around 13-24 demographic. The article states that most people who visit Tumblr will also be on the site much longer searching through pages. This is unlike Facebook and Twitter as people just take quick glances to see updates, and then log off. Tumblr provides much more engagement in the social world.
Posting during these times also never means that people will actually view company/individual posts. Posts that have some intrigue and sustenance tend to gain more retention from users. Posts should have some kind of information people need to know or learn about. Otherwise, users will just glance over the information and forget it right when they are done reading. Posting requires both timing and quality posts in order to be successful in the social scene.
Article: http://socialmediatoday.com/brett-williams/1017741/best-times-post-tumblr
-Darrik Marstaller