When to start off Tomato seeds

Just to use the same question & logic, what about Cucumbers - same dates ?

 

No. Cucumbers are nowhere near as tough as tomatoes. A month later is plenty soon enough.
My chilli seed will get started early February, tomato seed early March, Cucumbers, melons and squashes mid April. All timings are approximate dependent on weather, mood and workload.
The tomatoes and peppers will be in a cold greenhouse late march early April although in a cold spell they will come into the house at night and most nights will be covered with fleece or newspaper. Cucumbers, squashes and melons will go to the greenhouse early to mid May and the squashes outside end of May.
Mid April to May is when I start off the sweetcorn and runnerbeans in the cold greenhouse.