I recently did this in a campaign of mine and it... ruffled the DM's feathers to say the least.
Arcane Abeyance is a 10th level Arcane Tradition for the Chronurgy Wizard that allows the caster to condense a 4th level spell or lower into a "mote":
When you cast a spell using a spell slot of 4th level or lower, you can condense the spell's magic into a mote. The spell is frozen in time at the moment of casting and held within a gray bead for 1 hour. This bead is a Tiny object with AC 15 and 1 hit point, and it is immune to poison and psychic damage. When the duration ends, or if the bead is destroyed, it vanishes in a flash of light, and the spell is lost.
A creature holding the bead can use its action to release the spell within, whereupon the bead disappears. The spell uses your spell attack bonus and save DC, and the spell treats the creature who released it as the caster for all other purposes.
Emphasis mine. As one might tell from my profile, I'm a huge fan of the wonderfully balanced Leomund's Tiny Hut. The following occurred last night in our campaign:
Obnoxious, power-gaming Wizard and party come face to face with a horrible monster with many claws. With an initiative of 31 (because Chronurgy Wizard is wonderfully balanced), the Wizard releases his pre-prepared mote of Leomund's Tiny Hut and summons a hemispherical dome inside of the dungeon, blocking the exit with the party inside.
Because Leomund's Tiny Hut allows for objects to pass out of the barrier but not in, the party peppered to death the poor monster without it having any ability to respond while the Wizard smoked his pipe wistfully. The monster, having no magical ability whatsoever, proceeds to waste its turns digging and attempting to dodge as the party massacres the creature in its own home.
My question is, was the above situation legal, RAW? Is this really allowed and can Arcane Abeyance allow for spells with long cast times to be shortened to a single Action?