I love vegetable planners. Especially pictorial ones like this beautiful vegetable growing cheat sheet by Anglian Homes. They also provide an interactive version on the website.
This vegetable planner adds another dimension with its companion planting element.
Of course, nothing is black and white when it comes to gardening. There will be much flexibility in the times we sow, plant and harvest and we should do our best to understand our own allotments and gardens, letting the weather and soil conditions be our guide.