Flamestrike
Legend
Not DMing 5E currently, but I'd note there is a natural desire to have a long rest at the end of a session because as the GM you want to have some sort of climax and aftermath at the end of the session to make sure people end on a high note and help player engagement.
But equally, ending a session with the party depleted of resources, and needing to spend the week thinking of way to achieve the quests end-goal in their current state (and looking forward to the climax with the BBEG the following week) is also a valid method of player engagement.
Like, you'll do the opening conflict to draw people in, chance for PCs to do their thing(s), some setbacks, progress and some sort of climax for the episode, and the aftermath which sets up next sessions opening conflict.
Assuming this only involves 1-3 combat encounters, then there is no reason not to simply turn the end of session long rest into the end of session short rest. In fact, thats much closer to 5E's expected pacing.
Then again, that game is also not even close to 20-30 minutes a combat (to quote the GM when I mentioned that 'AHAHAHAHAHA, wait.. really?')
Shorter AD's (which your group seems to have) result in deadlier combats. Deadlier combats take longer to resolve by default (and in campaigns where they feature, long rest classes such as full Casters will show up a lot further slowing things down). Due to the deadly nature of the combats, all turns need to be fully optimised to ridiculous degrees, all actions planned out and all spells used at the precise time or else a TPK is just around the corner.
For example a combat featuring 8 Hobgoblins and 1 Hobgoblin captain is a 'Hard' encounter for 5 x 5th level PCs (just). This should not take more than 20 minutes to resolve (and much less time if the party Wizard has a fireball spell prepped and is prepared to blow one of his 3rd level slots on the encounter).
I would personally expect this encounter to drain resources (hit points, a barbarian rage, a fireball and a shield spell, a few cure wounds, maybe a sup dice or two to take down the Captain) but there should be no real chance of a PC death unless the Hobgoblins roll particularly well (initiative and then surround a PC). The threat is there, and its enough to make the party mage consider going for his highest level spell, but its a challenge that is workable by the party.
Now throw 6-8 such encounters this at them, forcing them to stretch those fireballs, rages, divine smites and sorcery points over the duration and it becomes a very different story indeed. Using rages, spell slots and so forth becomes a meaningful choice that affects the entire strategy for the whole adventure.
The overall challenge comes not from overcoming each individual encounter, but from overcoming each individual adventuring day.