The answer for the first would be late may if the weather is cooperative. This is because the longest amount of daylight of any 2 month period is from may 21st to july 21st peaking on the summer solstice of june 21st.
If your plant takes 8 weeks plant it around may 21st if it takes 10 weeks around may 13th. As long as the weather is ok. However if the weather is cool or damp wait till drier and warmer weather arrives.
I am not an expert in european climate as it is not my area but I do know bulgeria is almost completely medeteranian climate which means you have hot dry summers. So be sure to water your plants every week if not twice a week.
So in light of all that Id say plant your plants between may 15th and 30th and you will recieve the best yields. Happy Growing and Good Luck