Sucession planting takes planning. Days to maturity helps in planning when to plant and how much and an approx date for the next succession. But as others have mentioned other factors come in like the temperature and hours of daylight. Say something like lettuce. Looseleaf lettuce matures anywhere from 40-55 days after germination. So a guestimate would be planting seed by counting backward the average time say 45 days + 7 days for germination = plant seed 52 days before planned harvest. How much to plant depends on if you are going to harvest leaves in between and how much lettuce you can eat in that time frame. For me, I plant about 10-15 seeds to yield about 8-10 heads in 45 days. I will eat the outer leaves as they mature and pull everything before the head starts to ball up. For me that can be anywhere from 30-45 days depending on how hot it is. Hotter weather makes the lettuce tipburn and bolt faster. When it is in the 60's lettuce grows very slow and is smaller. Ideally, when the temperature is between 70-80 the lettuce grows the fastest and the biggest (March-May). After June it is not worth planting lettuce. I would plant successive crop of 10-15 seeds every 14-21 days for a continuous crop, but I usually stop planting lettuce from May -September because it is just not worth it.
Short crops are the hardest ones to plan. Take the number of days to maturity +- 7 days. Add the days to germination to determine your planting dates. Plant as many plants as you can eat in 7-14 days. Replant seeds every 2-3 weeks until you reach your planting window. There are planting guides like the ones on the Farmers' almanac. It tells you the best times to plant based on your last frost dates, but also takes into account the plants' tolerance to temperature. The start dates may be off a few days so you may have to fudge the starting dates a bit more.
You also need to be careful if you are planting a garden of different plants to make sure that everything does not come in at the same time. Asian greens like bok choy, and lettuce mature about the same time. So stagger them out so everything will not come in at the same time.
Peppers, tomato, eggplant, beans are warm weather and do best when the temperature approaches 70
They have repeat harvests so a few plants can provide for a while. Beans and peas produce for about a month. So you have to replant them every 2-3 weeks for a continuous harvest if you want them fresh.
Some things are seasonal and take a long time to mature like onions, cabbages, celery so it is important to start them at the right time of the year.
The hardest thing to do is to leave part of the garden empty so you have someplace to plant the succession crop. What you can do is plant a cover crop in the garden and till in the cover crop as you plant the new seeds or seedlings. Most cover crops peak at around 6 weeks but you can till them in earlier. If you like radishes you can plant them as a first crop since they mature in about 21 days.
You are not alone. I have this problem too, mainly planting more than I can eat in a given space of time. I forget that romaine lettuce, beets, carrots, and beans all mature around the same time. So, I have to space them out a week apart from each other so I have more time to harvest. It is why I prefer to grow longer crops that are more productive over a longer period of time. Green eggplant, swiss chard, kale, green onions, herbs, hot peppers, sweet potatoes, ginger, taro, and tomatoes. I usually plant tropical corn, eggplant, tomatoes, and NZ hot weather spinach in summer, they are the only things that can take the heat. July-August is the best time to solarize.
https://www.almanac.com/gardening/planti ... /MA/Boston