Who wants to be the first to create calendars for the planets of Trappist-1 with incredibly short years?
The article gives year lengths in terms of our day length, but since they're all presumed to be tidally locked, their rotation periods match their revolutions, and the days are effectively infinite.
I suspect a calendar system there, then would more likely track the orbits of the various planets in a similar way to how we track the 4 largest moons of Jupiter.
Yep, apparent position of the star permanently fixed, no other stars visible from the illuminated side, but the other planets are large and bright enough to see easily even in the daytime sky. Since they are locked in simple orbital resonances, their passages
could be used to reckon time, and they will often be seen to transit the star. The scale of the system is actually quite comparable to the Jovian system, although of course the star is appreciably larger than Jupiter. Strong inter-planetary tidal effects.
Probably negligible magnetospheres, therefore little protection against the star's coronal mass ejections, atmospheres probably stripped away (like that of Mars).