The only time parameter is Decay and can be adjusted manuall by means of the Dec. control in the range 2 ms ... 2 seconds. The attack time can be adjusted internally by means of a separate trimming potentiometer for each sub-unit in the range 1 ms ... 15 ms. The factory setting is about 3 ms. This is the attack time of the TB303. Each envelope output has a LED control available. The trigger inputs are normalized (1 -> 2 -> 3 -> 4). 

Suggestions for modifications:

• Each sub-unit has a pin header with two pins available. When the two pins are shortened (e.g. by means of a jumper or a toggle switch connected to the two pins) the corresponding sub-unit changes to a loop mode. In this mode the unit is triggered by itself like an LFO..
• By changing the value of a capacitor the time range can be modified (e.g. 0.2 ms ... 0.2 seconds or 20 ms ... 20 seconds)