I think the critters are your main worry - voles in particular. Voles are
quite capable of entering pots through their drain holes, so maybe cover
the drain holes with aluminum window screen or quarter inch hardware cloth
and enclose the top. I believe saffron is fairly forgiving wrt soil type
but don't have much direct knowledge. I have heard they grow fine in clay
soil with a slope for drainage, but no personal experience.
The voles care nothing for the flowers and foliage. Only the bulbs. With
this in mind, I have had success planting the bulbs 3" or more deep and
embedding half inch hardware cloth over the soil so it extends a foot or so
past the bulbs in every direction. The flowers and foliage seem to find
their way through the hardware cloth just fine and the method should
protect other similar bulbs with fine foliage too. Note, I use half inch
hardware cloth embedded in the soil or quarter inch above ground. Either
seems sufficient.
As far as planting time, I can't recall the exact date they will start
growing but they will bloom (at least the larger ones) sitting on a shelf
if you don't plant them in time and they will be pushing leaves at the same
time. I will plant mine toward the end of August to be safe.
Tim