I'm fairly certain (IDNHMBWM) that you are required to prepare and expend the spell for any scroll you wish to scribe. Thus, you can't scribe 40 first level spells in a day until such time as you can prepare 40 first level spells in a day.
My house rule is that, in one day, you may prepare scrolls of:
1 spell whose market value is less than or equal to 1,000 GP.
OR
A number of spell levels equal to or less than your spellcasting stat bonus.
This means that at low levels casterswith the scribe scroll feat can usually prepare multiple 1st or 2nd level scrolls in a single day. By mid levels, it is less of an advantage.
Note that I also allow preparing multiple doses of a potion in a similar manner.