From looking at the rules, I believe using suspend is governed by whatever type the card is, so if it's a creature type, you can only use suspend during a time you can normally cast a creature. If it's an Instant type, you can use suspend for that card when you can normally use an instant card, etc.
Untap, upkeep, Draw
Plains
Done
Rokapoke: 20
Hand: 2
Library: 29
Battlefield:
(TTU) Forest x3
(TT) Mountain x2
(U) Wild Nacatl (2/2; Cat Warrior; ~ gets +1/+1 as long as you control a Mountain. ~ gets +1/+1 as long as you control a Plains.)
(U) Nessian Courser (3/3; Centaur Warrior)
(U) Prodigal Pyromancer (1/1; Human Wizard; T: ~ deals 1 damage to target creature or player.)
Graveyard:
Exile: Nantuko Shaman (3/2; Insect Shaman; When ~ enters the battlefield, if you control no tapped lands, draw a card. Suspend 1 -- 2GG (Rather than cast this card from your hand, you may pay 2GG and exile it with a time counter on it. At the beginning of your upkeep, remove a time counter. When the last is removed, cast it without paying its mana cost. It has haste.))
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Spiderman: 16
Hand: 5
Library: 48
Battlefield:
(U,U) Swamp x2
(U,U,U) Plains x3
CoP: Green (1: The next time a green source of my choice would deal dmg to me this turn, prevent that dmg)
(U) Veteran Armorsmith (2/3; Other Soldier creatures I control get +0/+1)
Graveyard:
Exile: