Copy constructor and assignment operaters are created implicitly if they aren't defined explicitly (see
here). The sf::Time class has a default
copy constructor (aka compiler-generated copy constructor or implicitly generated copy constructor) and thus you can initialize it with a sf::Time object.
You could've also just tested it, it works fine.
#include <SFML/System.hpp>
class TR
{
public:
TR() :
m_tr(sf::milliseconds(200)) // Init with 200 ms
{
}
private:
sf::Time m_tr;
};
int main()
{
TR tr;
}