dnd 5e – Is there a way to accelerate or pre-cast spells with long casting times?

A 10th-level Wizard of the Chronurgy Magic Arcane Tradition from Explorer’s Guide to Wildemount gets this as a class feature, with the Arcane Abeyance feature allowing them to condense a spell of 4th level or lower into a mote that lasts for an hour and can be unleashed with an action, once per short rest.

This wouldn’t work for either of the spells you mention, though, since they are 8th and 5th level.

(I suspect any more general mechanisms to do this more generally are rare, nonexistent, or very hard to get in RAW, given that WotC apparently felt the need to constrain to “4th level or below” and “you can only save it for one hour” to make this balanced.)