Sessions sometimes have issues with pacing, in that it may feel drawn out or cramped. When plotting out a session, plan out certain moments in your story, and at what point they should happen (relative to play time). When you and the players are at the table and your session is about to begin, hit start on a stopwatch. Check the time on your stopwatch every now and then and have a look at your notes.
Did you introduce the friendly NPC after the first hour of playtime? No? Timebomb number one goes off and they run into the players. Did your players meet their nemesis by the two hour mark? Yes? Timebomb defused, if not, the next timebomb triggers and something happens to introduce them. Have they discovered, that the friendly NPC put the nemesis under a spell after 3 hours of play? No? Here goes timebomb number 3.
Personally I get frustrated, as a player and as gamemaster, if the story/game does not progress at a steady pace. There are some important exceptions, as for example if you want to frustrate your players in order to emphasize a following situation. Generally speaking, things should be happening in pen and paper games, players will be frustrated if their ideas/actions do not progress the game or if situations lose themselves in too much detail. Often the gamemaster is happy that their players are engaged and gives them a lot of space to act out the situation. Especially at the start of a session, when everyone still has a lot of energy, this can take up a sizeable amount of time. Usually the story does not progress (much) in this phase, stakes are low and players settle into their roles. When everyone is done, the questgiver comes by, the players leave their tavern or similar. I don't think this is a particularly interesting start to a session, as it doesn't provide much besides a way to talk to eachother for a bit. Time to break this habit (or blow it up with a cheesy timebomb)!
Let's start with a super simple plot that goes as follows (assuming your players are hero characters): Evil guy lays siege to the town your players are located currently, evil guy has a secret vulnerability the players must find out, evil guy must be defeated. The first timebomb would be: 00:15, explosion - introduce the evil guy, he wants all newborns from the last 6 months. So after your stopwatch hits 15 Minutes (plus/minus a few minutes if needed) something blows up close to the players, the evil guy rides into the scene, kills a few bystanders and proclaims to the audience (guards and players) that he expects them to deliver all the newborns by tomorrow or he blows up the entire town. He then leaves the scene. The towns chief will promise the players gold and fame for killing the evil guy. Players should now work on finding out who the guy is, where they can find him, and how they can beat him (or add any more complicated twists).
Think of a time, how long it should take to uncover this information, and how it can be uncovered (the "how" is a backup plan, in case the players don't come up with a good idea). Let's say an hour should do it, add a few extra minutes and here we have the second timebomb. 01:30, players should have found out, that the evil guy is vulnerable to silver weaponry. NPC from other town noticed how years ago the same evil guy was wounded by someone with a silver knife. Players should know that he camps next so waterfalls half an hour north of the town, a traveller saw a camp with a weird symbol.
This timebomb will be defused if the players have already found the information required to solve the situation. Ideally you will nudge them towards uncovering the information during playing time, but you have a backup in case you need to progress the story and a time that lets you know when that should happen. Finally the last timebomb is at 2:15, the showdown. If the players have no plan to confront the evil guy, the evil guy will confront the players. He simply got wind of them trying to find out about them and doesn't like that very much.
It helps structuring your session, doesn't take a lot of time and makes sure your story doesn't get stuck. As gamemasters, we sometimes tend to give players more room than we should. This can frustrate players often without the gamemaster noticing.
- Don't make too many, 3-5 per session is definitely more than enough.
- You should have a plot for the session, this is simply a way to structure that plot in a way that makes sure you also pace it.
- Players should be able to defuse some of the timebombs by uncovering information or solving tasks.
- Timebombs should not be confused with ticking clocks (ticking clocks are used to let the players know they have to do something in a certain timeframe before something happens)