The 88 has a lot of bomb selection controls.
First you need to open the bomb bay doors and the toggle command won't work for this because they are manually operated. Like all manually operated controls in the sim (eg the 109's flaps), you need separate open/close commands and you must keep the relevant button pressed until the operation completes. You'll know when the bomb bay is open by looking at the hand-crank on the copilot's side of the cockpit walls, when it stops turning you can stop pressing the button (similar for closing them, just keep pressing the key you mapped until the crank stops moving).
After that you need to select the bombs. I don't exactly recall the name of the commands in the options, but i just mapped keys to all bomb related commands and then tried them out in flight to see what they do.
So, what you need to do in the 88 is to first select which bombs to drop (external, front bay, rear bay, all), then select the salvo size. Then you can arm them, input your bombsight data and have a go at it.
In the case of dive bombing, it's still beneficial to input bombsight data if you want a specific pattern. The delay between bombs is measured in meters and not time (eg, milliseconds). That means, in order to get the spacing you want, the bombsight needs to know your altitude and TAS so that it can calculate the release intervals. If you have wrong altitude or TAS the interval will also be wrong.
Initially, you can just set them to release all at once in salvo mode. After 2-3 trial runs you'll know what kind of altitude you usually release from and what kind of speed you have at that point (just pause and look at your instruments just before release during your test runs). In your subsequent runs, you can then use this data.
For example, let's say i want to hit a row of three hangars so i don't want to drop them all in a salvo. I have a lot of small 50kg bombs and two bigger ones, so i select all bomb bays and set salvo size to maximum. I know that when i drop, i'm usually 1km high and doing 500 km/h. The altitude is low enough that IAS/TAS conversions are negligible and i have a lot of bombs to make up for any inaccuracy (especially since i'm also at low altitude and the error will not affect the bomb trajectory for a long time), so i just set bombsight altitude to 1000 and bombsight speed to 500 before i even start diving.
Then i select a suitable spacing. I have lots of bombs to "walk" over those hangars, i don't want them to "walk" past them and go to waste, so i select a small spacing. Let's say 5m or less (if it's even possible to go lower than 5m, i can't really remember). Again, this spacing is not a time interval but the calculated space between impact points on the ground.
Finally, i can roll over into the dive. A couple of seconds before reaching my chosen release altitude i can make a last second airspeed correction (input the current value into the bombsight) and release.
Hope it helps