###1. Carry pre-generated characters.
###2. Allow character changes after-the-fact.
- Pregenerated characters can save you a lot of time. It's not the ideal solution for immersive role-playing, but it'll save you what sounds like hours. Then, between sessions, allow the new player to build a character of similar level, now that they've got a taste for what they like or don't. I've got a stack of about 30 pregens* that I keep in my GM binder, so a new player can usually find something pretty-close to their idea and get rolling.
After the session the player can either keep the pregen, make modifications to it and keep playing it (see below), or make a new character from scratch now that they've some ideas. The pregen thus discarded could be worked into the narrative as an NPC or discarded as you see fit. (With thanks to @Cronax for the suggestion.)
- Many GMs allow players to make modifications to characters well after character creation. In Adventurers League it's everything down to race, class, and ability scores until level 4**. Others will make reasonable allowances for changing anything that hasn't factored majorly into gameplay. This question for helping new players make characters, and its answers, contains good guidance in this vein. I, personally, will allow pretty-major rebuilds at any level; my 5e table isn't much prone to "abusing" mechanics.***
* Some come from the WotC site, some from the defunct Wizards Forums. Others from "solitaire" play--rolling up characters for fun--and others were specifically built to provide character continuity from previous campaigns/systems.
** see page seven of the Adventurer's League Player's Guide, "Character Rebuilding"
*** In real life I play a character in a system where it's a very hard and long process to make these sorts of changes. I don't need to enforce that constraint on game-players.