I will allow my players to craft in incremental time (2 hrs one night, perhaps 5 hrs tomorrow) until the item is complete. The player just has to make allowances for this in game time. I also believe in downtime, and will be using it for many reasons other than just crafting.
I absolutely hate xp costs for creating items and spells. It just seems anathema to me. I decided to have the xp cost add to the next level cost for advancement, cumulative for each item crafted/spell cast that costs xp. Player crafts 3,000 xp worth of stuff and casts 1,000 xp worth of spells, then it will take an additional 4,000 xp past the current next level limit.
This way, the player doesn't lose any xp at all, it just makes the next level a bit further off.