Onsite at AthenaHealth, Waltham, MA

I have been invited for an onsite interview at AthenaHealth for the Software Engineer role. i have not yet provided my availability as I am figuring out, how much time will I need to prepare for it based on what the onsite comprises of. Any insights into how the onsite @athenahealth at usually runs, will be highly appreciated and greatly helpful to me. any tips, suggestions around preparation? TC: 72k YOE: 1.5yrs