As soon as he awakes, Brian Porrell checks his e-mail, sometimes firing off a message before he gets out of bed. He makes calls during his commute to the Waltham staffing firm WinterWyman, spends 10 to 12 hours at the office and out visiting clients, and keeps his phone by his side at night, checking work e-mails while he watches sports on TV. Like many workers today, Porrell, 30, is on the job wherever he is — and he doesn’t count out-of-office exchanges in his 50-plus hour week. The millennial generation, the first to grow up with smartphones in their...