Is it possible? Use actions between exploring active location and placing progress tokens on the current quest card?

I ask it by cause of the next situation:

1. Boromir leadership was in play with Visionaly leadership in play (so all gondors characters had +1 wp). All commited characters could win the game with all their wp (in the current quest phase of 3b card).

2. In quest it was revealed Druadan Elite (it had prowl 1 - and my heroes only had 1 resource, the one of Boromir-)

3. Active location was Garden of Poisons. With it in play you can't add extra resources (Boromir had Steward of Gondor attached - and not exhausted, of course -)

4. Within resources on Boromir i could explore location, but not win the game (not enough progress tokens on the 3b).

...so, the question is:

*** One time i have explored location, and before closing 3rd step of quest phase, can i use Stewards of Gondor and place 2 resources on Boromir and my gondor characters gain +1 wp, and..... win the game?

If I understand you correctly.. then no.. there is no action window while tokens are placed.

Progress tokens are placed in a single movement. All of them are placed in a single instant and there is no opportunity to do anything between placing on the location and the quest. This is why explored actions have "response"... not action. Also when a quest is completed all extra tokens are destroyed and quest cards instantly resolve and change tothe next one and resolve interrupting everything in the game.

There IS a action window at the end of the staging step before tokens are placed.. so after all staging cards are revealed and when reveled effects have triggered but before the progress is calculated. (see the coloured bars chart thing in the core manual)... this is a action window and you could tab steward to add +will at this time, and this would count.. .just as you can use protector of lorin or eoywens ability at this time.

So in short.. no.. your example will not work, as even though the location goes out of play, the threat has already been calculated.. all your doing is placing tokens.. and there is no action window here.