As of VL 1.1 this has been integrated, this should allow also really big lists to sent mails without hitting a timelimit of php. Though, it has yet to be tested on a larger list.
Note even though this should allow big lists to send mails without hitting a limit, a MAX MAILS PER HOUR limit of your host could still occur.
If you have a big list, ask your host before sending mails, so that you can do proper math and make use of the "send mail each xx seconds"