Proton multiple-quantum time-domain NMR combined with time-temperature superposition is a powerful method to study entangled chain dynamics. Overcoming the previous limitation to regimes II-IV of the tube model, this study extends the method to regime I (localized Rouse motions) by use of a pulse sequence adapted to shorter times, thus covering all relevant regimes for the model case of poly(butadiene) with molecular weights (M) between 10 and 200 kDa. We determine a value for the entanglement time that is consistent with current rheological results and confirm a value below 1 for the time scaling exponent of the segmental orientation autocorrelation function (OACF) in regime I previously observed by other NMR techniques. The origins of deviations from tube-model predictions are assessed by focusing on the dynamics of the chain centers in end-chain deuterated triblock samples and by dilution of probe chains to 15% in a deuterated matrix with M of 2 MDa. The study is complemented by self-diffusion coefficients measured by pulsed-gradient NMR. Our OACF-based results for the terminal time reinforce the current consensus that below a chain length of 30-50 entanglements matrix effects cannot explain the nonideal M-scaling exponent of 3.4 but are responsible for an M-independent slowdown. The protracted approach of the pure local-reptation scaling in regime II is found to be only somewhat reduced for both chain centers and chains in a long matrix, confirming its generic intrachain origin. These microscopic insights could be compared with results from large-scale computer simulations and provide a gauge for theoretical approaches such as those dealing with constraint release and contour-length fluctuations.