If it's an organic granular fertilizer, most products I've seen recommend to side dress every 30 days during the growing season. So, depending on the crop, this would be 0 to 3 side dressings. Keep the fertilizer a few inches from the stem & work it into the soil as best you can. Again, this is for a granular fertilizer. I don't have much experience with liquid fertilizers, but much of what I'll say is still relevant.
Aside from how long they take to mature, another factor is their feeding requirements. Some plants require more nutrients than others. For example, radish is a fast grower & a very light feeder. They don't require any special preparation or fertilizer. Many veggies are moderate to heavy feeders that need a good soil rich in compost and/or manure. They also like additional fertilizer throughout their growing season. Pick up a growing guide, or search the internet to find out what each plant's nutritional needs are.
Like DDFarm mentioned, be very careful about adding too much nitrogen, especially before they begin to flower. Like he said, you'll get big plants w/ little production.
Just to get you started...
Tomatoes: Heavy feeders. Side dress. Watch the nitrogen.
Bell Peppers: Moderate feeders. Wait until fruit set to side dress.
Cukes: Heavy feeders. Side dress.