Throughout the GTA 5 story, Lester will offer Franklin missions in which he'll have to assassinate a target. These targets have a huge role to play in the companies whose stocks are available for purchase, and their deaths will affect the value of their corresponding stock.
Stocks in the LCN network generally change with every in-game hour during the business day (around 8AM - 7PM) - usually it takes on full business day for an LCN stock to reach it's peak value after an assassination. The BAWSAQ stocks usually change every 10-15 minutes of real-world time, though after an assassination the values of the affected stocks are usually changed immediately.
Note : The percentage return for your stock is only detailed in the in-game web page called My Portfolio. To get the best return you may need to advance time in-game, which can be done 6-8 hours at a time when you enter the save menu next to a character's bed, then exiting the menu without saving. To maximize profits, be sure to create a save before starting an assassination mission so that if a peak value is missed it can be reclaimed.
1. The Hotel Assassination
At some point Lester will start providing Franklin with side missions marked with an L on the map now before you can move past the story at this point, you'll have to do The Hotel Assassination. In this case you are damaging the shares of Bilkington in order to raise the shares of Betta Pharmaceuticals.
Before the mission: Make sure it’s Monday. Switch between the characters and invest everything into Betta Pharmaceuticals (BET) using your phone.
After the mission: Wait for the return percentage to rise to 50%, then switch between the characters and sell everything. This should happen after about 18 hours. If you choose to advance time by saving, be sure to check after every save.
NOTE: The following information on Bilkington Pharmaceuticals applies only to players on PS3 / Xbox 360. The market values of the Hotel Assassination have been severely reduced in the PS4 / XB1 edititions.
Buy AFTER mission: [BIL] Bilkington (LCN)
Sell AFTER rebound: [BIL] Bilkington (LCN) at an 80%+ return
After you sell BET, don't buy BIL right away. In several in-game hours BIL price will drop to its minimum and will stay there for at least 2 days, that's when you buy it. Now comes a long period of waiting and sleeping in a safe house. It takes BIL a week to rebound back to $200+ price, thus giving you 80%+ return on investment (highest seen so far is 103.34%). Actual percentage depends of whether you buy right after selling BET or wait and whether you sell once BIL hits 80% or wait several hours more.
NOTE: This may be a glitch, but it is possible to get a return profit of over 100%. How to did this is that right after the mission, you should sell your [BET] stocks and then buy your [BIL] stocks. Your game should then auto-save. If it does, reload that autosave. As soon as it reloads, go ahead and go to your portfolio. If done right, the return should be way higher than 80%. But note that if you take too long in selling your [BIL] stock, the game will remember your last mission and put the stocks back down where it's supposed to go and will have to wait to get the 80%+ return. Here's a photo from Trevors phone on what your portfolio should look like if you did all of this right:
Before taking on any other assassination missions for Lester, complete the campaign mission "The Big Score" and finish the campaign. Depending on the outcome of your story, each character will have between $40M - $100M to invest in each stock that the following missions focus on.
2. The Multi-Target Assassination
Before the mission: Advance time until it’s Monday. Cycle through the characters and invest everything into Debonaire (DEB) on your phone.
After the mission: Wait for the return percentage to hit 80% (after about 8 hours), then sell everything. After that, buy as many Redwood (RWC) stocks as you can. The return percentage you’re looking for this time is a whooping 300%, which should happen sometime between 48 and 96 hours after you invest.
3. The Vice Assassination
Before the mission: Check the clock and see if it’s Monday. If not, advance time until it is. Invest all of your characters’ money in Fruit (FRT) using your phone’s browser.
After the mission: Wait for the return percentage of 50%, then sell (this should happen after 6 or so hours, so you shouldn’t advance time). Invest your freshly made cash into Facade (FAC). After 48 hours, the return percentage should be at 33%, which is when you should sell.
4. The Bus Assassination
Before the mission: Make sure it’s Monday. Do nothing else.
After the mission: Invest everything your guys own into Vapid (VAP) using your phone. Wait for a 100% return percentage, then sell. It should happen about 48 hours after you buy.
5. The Construction Assassination
Before the mission: Advance time until it’s Monday. Invest everything you have into Gold Coast (GCD) on your phone.
After the mission: Wait for about 24 hours, and look for an 80% return. Sell everything.