Concentrated Summoning (3.5e Feat)
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 Concentrated Summoning [General]
You can maintain the duration of a Conjuration (Summoning) spell through concentration.
Benefit: When you cast a summoning spell you continue concentrate on the spell, while concentrating you do not count time off its duration. After you stop concentrating, the normal duration resumes and then terminates as normal. You cannot resume concentration on a spell once you have lost concentration. You can only concentrate for this purpose for up to 1 hour.