Wizkids Rules!

Are Battle stations supposed to be called Before you roll your dice, or can you call them after you see what you have rolled?

The Steps of the Combat phase as found in the rulebook are:

1. Declare Target
2. Roll Attack Dice - The attacking player rolls their attack dice
3. Modify Attack Dice - The players spend tokens to modify the attack dice
4. Roll Defense Dice - The defending player rolls their defense dice
5. Modify Defense Dice - The players spend tokens to modify the defense dice.
6. Compare Results
7. Deal Damage

Whether rolling defense or attack dice, you first roll and then choose how you would like to modify the dice. Battlestations Tokens are used in the modify steps of the Combat phase.

Does this mean that Boheeka
"If your ship has a [Battle Stations] token beside it when you attack, you may convert 1 blank result into 1 [HIT] result"
must choose to either convert the blank result to a hit OR spend the [Battle Stations] token to convert all [Battle Stations] dice results to [HITS] (but not both)?

No, you may apply your modifications to the dice in any order you wish. In this case I would first use Boheeka to convert a blank to a hit and then spend the battlestation token to convert all Battlestations results to hits.