Ganesh is Pratham Pujya. Before any other deity is invoked the sankalp is placed before him, so that the vighnas standing in the way of the undertaking are cleared first. That is why his seva belongs at a beginning rather than in the middle of trouble.
The Special Pujas below are performed at the Ganesh kshetras of Ujjain — Chintaman Ganesh on the Kshipra, where he is worshipped as the remover of chinta in three forms, and Bada Ganesh near Mahakaleshwar. Modak and durva are offered in your naam-gotra on a tithi you choose.
14 sevas at 12 Teerth Kshetras — you choose the tithi.
Before the family begins living in the home, on a muhurta chosen for it. Where that is not possible, the seva is taken as soon after as the tithi allows. These sevas run on a devotee-chosen date, so the muhurta can be matched.
The 14 sevas here are Special Pujas — you choose the tithi yourself at checkout, so they are available year-round and are not tied to a fixed festival date.