24/48's without Kellys every third cycle suck, unless you sleep through most nights. Our schedule is a restructured 24/48. It's 24W, 24O, 24W, 24O, 24W, 96O. You get four day breaks three times a month. If you have to work a 56 hour week, I'd want my schedule. Some places will hold you over past your shift. With the 24/48, you can be held over for 12 or even 24 hours. Working a de facto 36/36 or 48/24 against your will will burn you out real quick. With the other schedule, you can't be held past 12 hours, for 36 total no matter what. Some CA FD's are doing a 48/96. I'd go for that, but not for an EMS only dept, since most are busy. You'd be traveling five times a month rather than ten, and you could even live 2-3 hours from work and be okay with that schedule.
If you're doing 12's for a 48 hour week, there's a three on, two off, two on, three off.
For a 42 hour week, there's 24's again, but in a much more desireable fashion: There's a 24/72, or 24W, 48O, 24W, 96O.
For a 40 hour week, there can be any combination of 8's, 12's, and doubles (16's). For example, you can do two 12's and two 8's, a 16 and two 12's, or five eights. North Shore LIJ Hospital in NYC has these combinations.
Some places also make three 12's a FT schedule, even though it's only 36 hours. That way, the company can give out up to four hours of late jobs a week on straight time.