The main aim of this work was to systematically investigate the effects of time on hydrothermal carbonization of holocellulose coming from the forestry residues. Based on the results, reaction time has a significant impact on the structural, chemical, fuel characteristics and combustion behavior of hydrochars. With increasing reaction time, holocellulose is gradually converted into the amorphous hydrochars with aromatic structure and abundant oxygen-containing functional groups; the O/C and H/C decrease from 0.85 and 1.60 to 0.23 and 0.71, respectively. The HHVs of some hydrochars have reached the quality grade of medium-high quantity calorific coal. The combustion stage and characteristic parameters of holocellulose are predominantly modified after HTC, and HC-14 could be regarded as a good fuel. Additionally, the structural and chemical formation processes of holocellulose-derived hydrochar are proposed. These results revealed that HTC is an effective and simple strategy for converting holocellulose into functional, value-added, and energy-dense hydrophobic solid fuels.