How would the volunteers at the Pilgrim's Office in Santiago possibly know if a pilgrim got two stamps for the day, five minutes apart, unless the pilgrim said so, or the volunteer could look it up in some kind of a sello database? Not likely, I think (even if such a database were possible), given the usual number of pilgrims waiting in line for their turn next, and the dozens and dozens of possible places to obtain sellos!
The two stamps per day rule is a bit of a pet peeve of mine because of the knots I've seen pilgrims tie themselves up into, worrying about it. A first-time pilgrim once tried to debate me on it, just outside Sarria, when I (wanting to reassure him) said I'd walked before and no one I knew of had ever had their stamps counted.
It's a bit tricky for me to relate to because I enjoy collecting sellos from various kinds of places and for different reasons, so I usually end up with more than two per day anyway (and two credentials to get from SJPP to Santiago).
But in all the times I've walked, seven so far, not once has my credential been looked at that closely. No one has counted my stamps. (If someone decides to in future, I'll watch with interest.)
To me it makes sense that the last stamp of the day would be from the place where you sleep, though I've often gotten sellos later in the day than that, from a museum or church or sometimes a shop.
But sellos don't have time stamps. (The photos I take all the way along do have time stamps though -- sometimes two or three minutes apart!)
Buen Camino! Have fun! And enjoy getting your sellos. I suspect you'll have plenty in the end.