I am an entrepreneur of a small software developer company. The flagship product is developed by myself and my company grew up to 14 people. One of pride is that we've never have to be invested or loaned.

The core development team is 5 people. 3 are seniors and 2 are juniors.

After the first release, we've received many issues from our customers. Most of them are bug issues, customization needs, usage questions and upgrade requests.

The issues from customers are incoming many times everyday, so it takes little time or much time of our developers. Because of our product is a software development kit(SDK) so most of questions can be answered only from our developers. And, for resolving bug issues, developers must be involved. Estimating time to resolve bug is hard. I fully understand it. However, our developers insist they cannot set the any due date of each project because they are busy doing technical supports and bug fixes by issues from customers everyday. Of course, they never do overwork.

I suggested them an idea to divide the team into two parts: one for focusing on development by milestones, other for doing technical supports and bug fixes without setting due days. Then we could announce release plan officially. After the finish of release, two parts exchange the role for next milestone.

However, they say they "NO, because it is impossible to share knowledge and design document fully." They still say they cannot set the release date and they request me to alter the due date flexibly. They does not fix the due date of each milestone. Fortunately, our company is not loaned and invested so we are not chocked. But I think it is bad idea to keep this situation. I know the story of ant and grasshopper.

Our customers are tired of waiting forever of our release date. Companies consume limited time and money. If flexible due date without limit could be acceptable, could they accept flexible salary day?

What is the root cause of our problem? All that I want is to fix and achieve precisely due date of each milestone without losing frequent technical supports.

I think there must be solution for this situation. Please answer me.

Thanks in advance.

PS. Our tools and ways of project management are Trello, Mantis-like issue tracker, shared calendar software and scrum(collected cards into series of 'small and high completeness' projects).