The objective is to cast a long casting time spells like Tiny Hut or Private Sanctum that can give you a battlefield advantage.
For example Tiny Hut allows your team to have a position from which you and your allies can shoot ranged weapons without being counterattacked by spells or weapons, Private Sanctum can deprive opponents that can teleport from doing so, or create a visibility shield around a fortification with siege weapons you plan to attack with a larger force.
Normally the casting time prevents the use of these spells in combat.
Assume you know where the opponents are. The challenge is to cast the spell close enough to them so the spell will help in combat, without being detected before you are done casting.
Ideal would be solutions that work with just the core classes, feats or spells from the PHB, do not need to rely on optional rules, and that also do not require access to specific magic items. (Although other solutions are also OK).
Is there a way to do this?
Best Answer
You say:
So you would like to close on the enemy, then cast tiny hut for example, as a way to gain a tactical advantage.
I think your spells are examples of preparing favorable terrain. Sure, you could use spells, but digging trenches or throwing up walls would have the same general effect.
Tiny hut is problematic because it takes so long, so it will only work in limited situations.
Don't take the favorable terrain to the enemy, bring the enemy to the favorable terrain
Prep your terrain, then lure the enemy.
This could be as simple as retreating until you reach your favorably prepared terrain.
This can be ideal because you can conceivably have significant time to prepare, from a minute to cast tiny hut to much longer for more elaborate preparations.
Limitations: you need to know ahead of time when and where the battle will be; you need to lure the enemy.
Use illusion
You might be able to use illusion to disguise what's going on or create a distraction.
Major image could give you an obscuring illusion, such as of a herd of cattle or similar, to obscure the sight and sound of your caster. Alternatively, you might be able to create an illusion to focus their attention elsewhere. A "dragon" attacking might give you a round or two to prepare terrain.
Hallucinatory terrain might be able to confuse the enemy enough that while they may hear the caster, they can't see them.
Limitations: Costs spells, you may not have these spells available. Maybe the enemy will catch on.
Use distraction
Get someone else (either in the party or not) to attack them from the other side. Maybe they'll the too busy to attack you.
Limitations: Requires the cooperation of someone else. And maybe they won't be too busy to attack you.
Time stop
Time stop is made for this. You get 2-5 turns to prep your terrain.
Limitations: 9th level spell, and if it were available to you, maybe you have better options. Roll badly and you just burned your slot for a measly 2 rounds of prep.
Conclusion
No tactic will work in every situation, and this is no different. But these might be situationally useful.