The majority of mainstream Protestant churches in the U.S. proclaim this age is the only opportunity for salvation. There's a prominent minority, mostly non-denominational, that claim the period after the second resurrection is another opportunity for salvation.
The implications today concern evangelism efforts. My experience with Baptist churches are they need to reach people before they die in THIS age, otherwise they are lost forever. My experience with the non-denominational churches (who believe otherwise) are many simply are not called in this age (e.g. John 6:44), they will be given a chance for salvation in the second resurrection (e.g. Rev 20:5, barring the obvious that those who've received, then rejected Christ, are impossible to redeem thereafter, e.g. Heb 6:6).
Although I was reared around the Baptist and Methodist churches, I don't know their scriptural basis for their belief if you die in the life never knowing Christ you are lost forever. The churches proclaiming that is not the case point out a lot of scriptural support.
the Lev 23 Holy Days, an annual reminder of the milestones in God's annual plan of salvation for mankind. For example, TO THE DAY Christ was crucified on Passover, TO THE DAY the Holy Spirit was made widely available to mankind on Pentecost. To come: Trumpets (Christ's return), Atonement (Satan's binding), the Feast of Tabernacles (1,000 year of Christ on earth), and the Last Great Day (8th day of Tabernacles, is the Great White Throne Judgement).
birthright and firstfruits theme throughout scripture. This is way too long to post here. But, I'll reply if requested. But, it is throughout scripture from Genesis to Revelations.
lots of scripture showing God is not calling everyone in this age, even causing them to be spiritually blind and deaf so that they cannot respond to the gospel.
and various other scriptures supporting this, e.g. Isaiah 49:8's proper translation is "a" day of salvation, not "the" day.
My question: what is the Baptist/Methodist/same Protestant scriptural basis the age we are currently living in is the only age for salvation?