A timestamp can only prove the time of your work. A timestamp cannot directly prove the ownership. If there is no equivalent or stronger evidence than yours which is timestamped the person having the timestamped evidence will be recognized as the owner of the work.
We can use a notary example for better understanding;
Normally, a document that is notarized has personal information and date information which means ownership as well as date evidence as shown. For example, any notary has notarized your document without your identity information but has only included date information. In this case, whoever has the document whose date of production is proven has conclusive evidence. Although the ownership cannot be proven by a notary, he/she who has the notarized document will be recognized as the owner of the document as there is no evidence demonstrating that the document had been done previously by someone else, so it is a similar situation for a timestamp as well.
We provide you with an extra secure feature which is Zip (Security) Signature. In case Zip File and hash value change hands of a third person, ownership and conclusive evidence may change hands (on condition that you do not have a copy). However, no one can claim ownership if the information indicating your identity is found in the Timestamped Zip File, in which case the third person would have to explain why he/she used your identity information while timestamping. In other words, even if a third person acquires the Timestamped Zip File and a hash value from your computer or cloud account he/she cannot claim ownership due to Security Signature feature.