Right now, Comair has F.O.'s who have only been on reserve for two or three months after finishing I.O.E., prior to being awarded Continuous Duty (High Speed, Stand Up Overnights, Illegals, Naps, whatever your company calls them) lines. It appears that eight months is what it's currently taking to consistently hold a more "normal" line.
Some of the tougher CD lines go junior. The more desirable ones (90+ hours' pay for 16 hours' flying) obviously go more senior.
Comair has everything from one-day trips to five-day trips. Some of the longer trips are more commutable than others. Pilots are able to drop, add, and trade trips as necessary most of the time to enhance their schedule. This month, one relatively junior (7 months with the company) F.O. got a normal line that gave him 15 days off - although this was abnormal for someone that junior.
How long reserve will last depends entirely on attrition (next to none) and how much the company is growing. Comair has hired over 170 pilots so far this year - though the bulk of that was in the first three months. Those who started in January will get lines in less time than those who started in July, unless Comair goes on another hiring binge, and the flying increases dramatically. Remember, the last pilot hired will be on reserve until the airline starts growing or hiring again, which could be a long time for some.
As far as for how many days you can expect to have off between trips, Surplus1 can probably give you a better idea about that, since he's been at Comair longer.
Off the subject a little - I flew an airplane yesterday that had 13.8 hours on the hobbs meter when we left CVG.
Regards
V-1