I think that for the delay to occur you might need to extend the reconquista, not just for Castille-Leon but for Portugal as well. A resurgent Granada
That's highly unlikly : since its creation, Granada was either under castillan domination or morrocean. Each time they tried to refuse Christians their tribute, the latter raided it and took another piece of land while Morrocean agreed to help in exchange of vassalisation (and not reallt helped them)..
The only thing that gave Nasrids enough time to survive up to 1492 were the infighting in Castille.
For the survival of another taifa, it's as well doubtful. The only thing that could have prevented the takeover of these regions by Castille would have been a Merinid takeover (more than the unfortunate campaigns they did OTL) before Christians can swallow it up (at best, Granada and Sevilla). Eventually, I don't see them doing much better than other berber dynasties (it could admittedly limit or butterfly the christian conquests in Morocco at the end of XV century).
They simply didn't have the same ressources (military, critically) or enjoying enough stability that being placed on trade roads would have been a critical advantage.
Bear in mind, it wasn't until Ferdinand and Isabella expelled the Granadan Emirs that they accepted to fund Columbus, and that was in response to de Gama and his route to India. Keep both of them distracted and it delays discovery to the end of the reconquista and its after effects.
This is chronologically wrong.
Colombus first expedition began in 1492.
Vasco first expedition began in 1497
Finally, the continental reconquista of Portugal (you can argue that Reconquista wasn't convieved as to be limited to iberic peninsula) was achieved in the XIII century, almost 200 years before Castillan one. It gave portuguese plenty of time to develop interest into atlantic navigation and partially explain their advance on it.