Yes you can Extend True Strike, but it works otherwise then you suggest. You got then 2 rounds to make your _one_ True Strike instead of one. See spell
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True Strike
Divination
Level: Sor/Wiz 1
Components: V, F
Casting Time: 1 action
Range: Personal
Target: The character
Duration: 1 round
The character gains temporary, intuitive insight into the immediate future during the character's next attack. The character's next single attack roll (within the duration of the spell) gains a +20 insight bonus. Additionally, the character is not affected by the miss chance that applies to attacks against a concealed target.
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As you can read you can extend the duration (from 1 round to 2 rounds) but not the number. Its fixed in the discription of the spell.
Have fun,
Laiyna
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True Strike
Divination
Level: Sor/Wiz 1
Components: V, F
Casting Time: 1 action
Range: Personal
Target: The character
Duration: 1 round
The character gains temporary, intuitive insight into the immediate future during the character's next attack. The character's next single attack roll (within the duration of the spell) gains a +20 insight bonus. Additionally, the character is not affected by the miss chance that applies to attacks against a concealed target.
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As you can read you can extend the duration (from 1 round to 2 rounds) but not the number. Its fixed in the discription of the spell.
Have fun,
Laiyna