No, No, no. The witch or any other caster can attempt up to one touch per level (assuming they can reach that many targets) during the round of casting. After that the spell is expended and unused touches are lost. This is pretty clear from the PRD.
PRD: "Touch Spells and Holding the Charge: In most cases, if you don't discharge a touch spell on the round you cast it, you can hold the charge (postpone the discharge of the spell) indefinitely. You can make touch attacks round after round until the spell is discharged. If you cast another spell, the touch spell dissipates.
Some touch spells allow you to touch multiple targets as part of the spell. You can't hold the charge of such a spell; you must touch all targets of the spell in the same round that you finish casting the spell."
You must touch all targets of the spell in the same round that you finish casting the spell. Pretty succinct.