If you have a partner, twice a week. I would take full advantage of partner drills. Most guys typically work rounds, not minutes, we work 3 minute rounds with 30 secs rest to work try to get quicker recoveries (instead of a minute). Go in to each session with some ideas about what you are trying to improve on (counter rights, inside work, pivots)

3 rounds shadow or rope to warm up
2-3 rounds mitts each (so that will take six) work on different combinations, pivots, whatever but focus on a skill. You can also work power shots with the larger square pad.
4 rounds drills (head gear/mouth guard), one guy works offense, one guy defense and switch, one guy may work jabs the other guy jab slips, or you can alternate, one guy throws a 1-2-3, the other slips, anchors and counters, you can add complexity. or work catching and countering or parrying,
3-4 rounds of sparring (with a purpose)
couple of rounds of calisthenics or ab work