Time plays a particular role in determining the relevant market. Firstly, a market may only exist for a specified period of time in the absence of substitutability of products or services offered during that period. Where the relevant market is transitory in nature, as in the case of public service delegation, the dominant position of an undertaking must be assessed in the market related to the markets concerned by the delegation, where the undertaking operates on a more continuous basis. Secondly, the market definition may vary over time as the characteristics of the products and services evolve and as substitution possibilities, particularly on the demand side, change. The determination of the relevant market, which is not static, may therefore, as the case may be, reflect technological developments, regardless of the definitions previously adopted by the various authorities. Thus, the passage of time may impede the delineation of a relevant market when demand-side substitutability can no longer be analyzed for the period covered by the notified objection, since the contemporary perception of market players of the possibilities of substitution offered to them, or which they considered as such almost a decade ago, is no longer sufficiently reliable.