That is the difference between a clock that drifts on a hot dashboard and one that holds the ±10 ppm stability window through a summer heat soak. The base product number is DSC1001; the full suffix DI5-066.5800T encodes the stability grade, temperature range, and packaging.
4-SMD, No Lead package, 2.50 mm x 2.00 mm footprint, 0.90 mm seated height. The 0.098" x 0.079" land pattern matches industry-standard 2.5x2.0 mm oscillator pads — no special footprint needed. Surface-mount reflow profile is standard SAC305; no moisture sensitivity level concern for a ceramic MEMS package. Tape & Reel (TR) packaging — the 'T' suffix. The part is also orderable in cut-tape or partial reel through distribution.