This is a perfect fit. Both products are really well done and incredibly polished. I've repeatedly asked the Respondly team to build Buffer-like scheduling into their product so I'm really excited to see them combine.
Respondly brands itself as the "The Fastest Way to Tackle Twitter as a Team" so not sure when it makes sense to schedule replies.
I'm just wondering what use case you have in mind for this. Like, when do you not want to respond instantly to a customer?