Another "file is colossal/rendering for ages" post (from after effects to media encoder)

[soc77640112]

I've read multiple discussion posts and watched youtube videos about exporting after effects projects.
Still not sure what I'm doing wrong. 8 second video takes nearly half an hour, I can't even see an estimated file size.

Format is H.264, I'm using Match Source - Adaptive Medium Bitrate (instead of Match Source - High Bitrate)
I'm worried because I have a major project coming up and if it takes half an hour to render an 8 second video, I'm screwed. 
  

[soc77640112]

Update - taking longer than expected:

[soc77640112]

Final file size: 23.3 MB 

Better than ending up with a GB but the video is only 8 seconds 

and it took 30 minutes