30 mins SLA for 1 customer means you are almost working for them exclusively if you are 1 man team. So they better be paying six figures or it is a no deal. Are they paying six figures ? Unless you have a support team, don't do SLAs especially that short of a window.

If you really want this business but don't want to hire a support team member, negotiate a different SLA which is not 30 mins. More like 24 hours. But then I don't know how mission critical this app is for the customer.