Sorry if I failed to express the things in a way to understand my situation completely. But even though your answer helped already, thanks.
I did not expect that i can apply 30/45 days prior ... I had a shorter period in mind.
30 days would work, 45 days would be great for me, no stress. Could you do me another favour and explain to me why you wrote "30/45 days"? When do 45 days apply?
And I did not know, that presenting a flight ticket could even help.
I have to go to the Immigration in Lampang.