There is only ONE way to instantly finish construction(s) and/or research.
When construction is already started and/or when the research is already in process, a gold button appears. To instantly finish press the “complete construction immediately” button.
A confirmation window will open and after confirming, all running constructions together with all researches in the village are completed in an instant. This instant completion costs 2 gold.
Note: Residence and Palace are excluded from this function! Also, keep in mind, that celebrations, demolition, buildings in the master builders queue or training of any troops are neither research nor construction.