One can call the Mother anytime and everything, before and after and during the work, before or during a difficulty (though it is never a good thing to anticipate ). In fact it is the experience of all mystics that if we call the Divine when things are fine then more often than not one is able to evade suffering. It is a question of building a living bond with the Divine, a bond of love and surrender. It is not a good thing to anticipate difficulties. It often acts like an open invitation to them.