I can't answer for Air Guard pilots, but I can for Naval Reserve pilots. I spent one or two weekends a month (sometimes more) flying for the Navy, plus a few consecutive weeks per year. I had a commitment to fly X hours per month. Sometimes I could do that on one weekend. Sometimes it took multiple weekends. Sometimes it took a "long" weekend. To maximize my flying time when drilling I made sure I kept in touch with the squadron maintenance officer to ensure jets were available the weekend I was planning to drill, and with the squadron ops and training officers to make sure I got on the flight schedule. I also drilled for 4 to 6 consecutive weeks during the year. I was fortunate to work for a major aerospace company who was very good about giving me time off to drill.
But it also depends on the "level" of your reserve status. There's the "Ready Reserve" and the "Standby Reserve". Ready Reserve is further divided into Selected Reserve and the Individual Ready Reserve. In the Navy there are also TARs (Reservists serving on active duty.) I don't know, but I would guess the Air Guard is similar.