Paper materials exhibit time-dependent elastic behavior [1] that greatly affects their long-term performance, but whose determinants are still poorly understood. To improve this situation, a continuum-micromechanics-based theoretical model for the elasticity of paper sheets, which has undergone a very comprehensive experimental validation, is herein adapted to deal with the (non-ageing) linear viscoelasticity of such sheets. Thereby, experimental determinations on the viscoelastic properties of lignin (a universal, nanoscopic constituent of paper sheets), indicating that they follow Burgers-like rheological behavior, and a multitude of previously estimated properties of other, multiscale constituents of paper sheets made of mean, softwood-based, unbeaten, chemical pulp fibers, are employed to theoretically predict, in the Laplace-Carson transform domain (based on the “correspondence principle”), homogenized relaxation and creep tensors of a paper sheet made of a typical volume fraction of the aforementioned type of fibers; before the latter tensors are back-transformed into the (physically relevant) time domain, through the famous, multi-precision, Gaver-Wynn-Rho algorithm. The resulting relaxation and creep functions, given in terms of relations between time and relaxation and creep moduli, agree outstandingly well with respective, experimentally determined relations that are currently available [2]. As hemicellulose and amorphous cellulose are both non-crystalline, hydrophilic polymers, they are likely to exhibit viscoelastic properties following Burgers-like (or similar) rheological behavior as well; in which case, corresponding, viscoelastic formulations may readily enter the proposed theoretical model and offer an even richer explanation of time-dependent elasticity, not only of paper sheets, but also of its constituent polymer blend, pulp fibers, and cellulose fibrils. The reported results motivate additional developments in viscoelasticity as well as viscoelastoplasticity of paper materials (possibly in the framework of “extended transformation field analysis”), further paving the way to theory-assisted, more accurate and reliable, production, research and development, as well as use of such materials.