One of the grates difficulties arising within the attempts to reconcile the quantum theory and general relativity stems from the profound differences in the ways the notions of space, time, reference frame, and causation enter the two formulations. It is often argued that both theories should compromise on their respective understandings for this merging (in the theory of quantum gravity) to be possible. Motivated by this thought, in the thesis we will focus on the assumptions brought up within the newly established framework of quantum causality and the formulation of time within the conditional probabilistic approach (so-called Page-Wotters formalism). With these extensions, there are already strong conceptual differences at the level of comparison between quantum mechanics and quantum field theory, the resolution of which would represent a preliminary step towards the ideas of quantum gravity. Stirred by this friction, the goal of the dissertation was to re-examine the notions of temporal and causal ordering in the context of modern approaches to quantum theory in relation to approaches within perturbative field theory. As an interesting playground for challenging our understanding we took time ordering operator and investigated it in several different, albeit related contexts: (1) as it appears in the Schrödinger solution of standard quantum mechanics with time dependent Hamiltonian, (2) in Page-Wotters formalism, considering a constraint equation with several quantum clocks and (3) in the context of quantum field theory and Feynman propagator. The research objective was to understand whether one can view the action of the time ordering operator as enabling a superposition of different time-ordered configurations, introducing time indefiniteness in the aforementioned settings. Regarding quantum fields, we questioned the possibility of the operational interpretation of the (scattering theory) virtual particle exchange process, often understood in terms of two time-ordered processes happening via particle/antiparticle exchange. Our approach was to look at the time-ordered exponentials up to the second order and attempt to isolate one of the ordering ’branches,’ projecting a superposition to a definite state. We found that one cannot break the time ordering superposition of the exponential expansion in the context of standard quantum mechanics coupling it with the ancilla potential; however, one can perform this kind of projection in the context of timeless quantum mechanics with two or more quantum clocks. We then approached these considerations in the context of quantum fields, using the Schrödinger functional representation, seeking to implement the Page-Wotters approach and the previously developed toy model.