Reasonable expectations when scheduling an promising delivery/ With teams that perform support functions as well as development never schedule more that 6.25 hours of development work per day.
Take a project that is 100 hrs. unless the resource (s) is 100% deidcated with no distraction calendar time for those 100 hours isn't 2.5 weeks, but rather more a month (average 4.2 weeks) the key is to get the project done right the first time and not let the business pressure you in to doing an half assed job. It's their job for their clients, but if you give in you are letting your team down and the business over all. So much to say on this topic . . .