probably too early. OR there are just that day works/diversions/whatever (strikes are rare-thats more for FRance). Just as for SNCF it is extremely rare to trains be full so long ahead-and certainly in that part of this world. You likely stay a day or 2-3 i Praha, the golden city? This age old trick was known to all young Railers long ago and seems to have gone the way down the drain since; on ARRival there do not rush right out of shopping centre=station, but go to counter (lower floor) and find tight window and show pass-tell wishes-and let them arrange it. They are extremely well used to that.

And even if, when, -there will be ALternaives, by day or via other ways.

OR is it maybe a LEO=private train ? If so-just check how cheap normal tickets are-around 10€.

Thank you for your answer! 

I just found a czech website that sells the ticket https://www.cd.cz/en/spojeni-a-jizdenka/spojeni-tam/fb296d5a-c8ce-4716-9f36-299f9d95fbe2 but i don’t know if it is sure or not. Or is it better to do as you say and book when arriving to Praha ? You guys asnwer really fast, it is super nice of you thank you again. 

I just found a czech website that sells the ticket https://www.cd.cz/en/spojeni-a-jizdenka/spojeni-tam/fb296d5a-c8ce-4716-9f36-299f9d95fbe2 but i don’t know if it is sure or not. Or is it better to do as you say and book when arriving to Praha ? You guys asnwer really fast, it is super nice of you thank you again. 
 

The CZ website is perfectly ok to book at.