Good news: Coleader can help you walk and chew gum, if by "walk and chew gum" you mean "do two things at once during your Session".
Doing so is super easy:
Add the first concurrent Block wherever you'd like in your Session, setting whatever Duration you need.
For the second concurrent Block, add it just under the first, and set the Duration of the Block to "0"
Easy peezy! Now you have two Blocks for two different items, starting at the same time, and not impacting the total Session length (which Coleader calculates automatically).