Indeed 30 is OK . Voted for that number in the poll.
Last week I was really shocked when I saw 60 levels had to be solved. Nice for crushers who can play constantly but I think 30 levels is a far better balance for players that have limited amount of time.
Thanks for tagging me @Sukanta_Biswas! Well @Jelly Jenny to be honest, 30 levels is enough for me... I don't know how people are going to complete 60 levels for a week!