How can I check how many DMs can be sent via API

[vicconsulting]

In my application I’m sending DM to every new follower.
There is a daily limitation of 250 DMs.
Please note user may also sent DMs manually via twitter.com , meaning I cannot just count how many DMs were send for given user today by my app only.

My questions are:

1. How can I check how many DMs still can be sent
2. When DM counter gets reset (what time and what timezone)?
3. If my app hits the limit and receives error that we cannot send that many DMs, will this push the app into sandbox?

Thanks