Can you cast a spell with suspend from your hand or only from exile?

Suspend can only be activated when the card is in your hand, but the spell itself is never cast from your hand via suspend. Instead, activating suspend exiles the card with time counters on it. The actual casting happens later, from exile, when the last time counter is removed (CR 702.62).

Here is the sequence: You may pay the suspend cost while the card is in your hand during your main phase (CR 702.62b). This is a special action, not casting a spell — it simply exiles the card face-up with the specified number of time counters. No spell is placed on the stack at this point.

At the beginning of each of your upkeeps, you remove one time counter from each suspended card you own (CR 702.62c). When the last time counter is removed, you must cast the spell without paying its mana cost (CR 702.62d). That casting happens from exile, not from your hand.

Importantly, suspend does not give a card the ability to be cast from exile at any time — it is only cast when the triggered ability from removing the final counter resolves. You cannot simply pay the suspend cost and then immediately cast it from exile by choice.

Example: You have Ancestral Vision in hand. You pay its suspend cost of 0 (just activating the special action), exiling it with 4 time counters. Over the next 4 upkeeps the counters are removed one by one. On the upkeep when the last counter comes off, a triggered ability fires and you cast Ancestral Vision for free from exile — never from your hand.