Most games I've played in or run, the game session ended around the time we wrapped up an adventure and doled out Karma, or just when we plain ran out of time. But most times the session was planned to end when the adventure wrapped.

Our groups would also usually be short on legwork, sometimes very short as in basically none. Probably the group that did the most legwork was one where the GMs wife played in the game. Maybe she was good at legwork, or maybe she got a hint ahead of time about what the next run would be and had time, like about a week, to think of possible avenues for legwork. I'd hate to think she was a GM mole who was there to help us along, lol.

This got me to thinking about the time to end a game session. Why not end it after the first meet and the job is described? You say 'X' amount of time has passed since the last run and the new meet. You break and the players are still sort of basking in the glow of a job completed, but they also now have the gears turning on planning for the next run. The next game session starts off with the players describing how their PC used karma (including how they in character spent it), healed, shopped, etcetera. This also helps everyone 'get into character'. Then transition into how they are going to go about legwork. Too, they may already have outlined some general plans and and know some items they may need to acquire to pull it off, so it avoids simple mistakes like going into the sewers with no light source.

This seems like a way for better shadowruns, not having Plan A fall apart at first contact and resulting in the GMs carefully planned story getting shot to pieces or blown up, the default Plan B.

I try and run things in a half and half way; the first half (or two thirds) of the session is the main chunk of the last run, infiltration, combat etc. Then, assuming we still have time, they get paid, get karma, and then get the meet for the next run - downtime can either be sorted in this session (players usually know what they want to do in advance), or worked out later. The advantage to having the meet and maybe initial legwork for the next run at the end of the session is that players can start throwing plans around, but get to sit on them for a week or so and think through any flaws. As a GM, it also means I don't have to write a ton of possible ways they might do each run, most of which won't get used when they make their choice of tactics, stealthy or loud, etc. - they can tell me the approach they want to take, which contacts they want to talk to and what they want from them, and I can work out the fine details of the run based on that.

I like. Sounds like it could simplify GM planning, and also better player plans.

I've experienced a lack of legwork leading to poor plans. So you are doing the obvious legwork leads, then breaking?

Could be interesting in some situations. I see three potential problems:
- If sessions are too far apart, players might need to be reminded of everything at the beginning of the next session.
- It only works if the players can really plan something after getting the mission. If the situation suddenly changes soon after the meet "the painting is getting moved out of the museum!", "terrorist are attacking the site" the players will be frustrated if they've been thinking about a plan just to discover that it doesn't work.
- I already have trouble wrapping up in time, having time left to introduce the next run would be quite a challenge. Especially since the meet always takes much longer than expected.

Personally, I'd rather follow another pattern:
Session1: Downtime, meet, basic legwork, end session
If there's a need for planning, you can then tell the players to do it
Session2: Action!

This has the advantage of starting a new adventure with the downtime, which gives time to the players to get back in character.

But that being said, the more I play the less I enjoy lengthy planning session. I'd rather use a mechanism with ad-hoc/post-hoc justification

That is sort of the same break points, just an extra break.

I currently have a problem around this.

Our group is pretty unstable so if I set anything up towards the end of a session, like give them their next mission or if we have to end a session in the middle of a situation like combat then we need to get the same players back together to pick up where we left off or people can get annoyed at missing out on the end of something they started.

Although we only tend to get in 3-4 hour sessions at a time I think I'm going to have to try and make every session stand alone.