I understand that your question trouble your soul. Understanding Christianity is never an easy business, on the contrary.
In Christianity there is what is important, and what is less important. The Gospel message is what is the most important:
- We were created by God to enjoy a relationship with him
- Adam sinned and plunged humanity under the wrath of God
- God reestablish the relationship through Christ
- Grace is given to those who accept his gift
- Christ is coming again not as a servant, but as a savior
These five points would be a brief summary of the core of the Gospel. There is a lot of discussion about what is the Gospel in our time:
What is the Gospel by Greg Gilbert, I think MacArthur
Ashamed of the Gospel would touch the subject, also on the web the The Gospel Coalition has many articles on salvation.
That beeing said, using the ancient terminology or our current time description is, in my view an amoral decision. Use the terminology that people around you will understand. When Paul preached in Athens (Acts 17), he used the Greek philosophy to start where his audience was.
The seasons fall under the same type of discussion, it is a question of preference. On less your salvation comes from your ability to follow any type of law. As shown in the verses below.
Galatian 4.9 But now that you have come to know God, or rather to be known by God, how can you turn back again to the weak and worthless elementary principles of the world, whose slaves you want to be once more? 10 You observe days and months and seasons and years! 11 I am afraid I may have labored over you in vain. (ESV)
The Holy Bible: English Standard Version. 2001 (Ga 4:9–11). Wheaton: Standard Bible Society.
After reading the moderator comments I'll try to be more specific on how I believe my answer ties in with the questions. Here are the question asked in the post:
Which timing is correct/Scriptural?
The way we speak of timing is not a moral issue, and not a Gospel issue. Therefore I would argue to use the language people around you would understand. Is is more a practical issue then a theological issue.
Changing the times and seasons rings a bell in my mind but I do not remember which verse. When the Anti-Christ comes doesn't he change the time, etc?
Without a precise context that question is very ambiguous. Time can be understood in different ways in this questions. 1. Time, has the way we live (a technological time/age) 2. Time a the way we understand the history. Changing what we believed happened in the past. (The second world war, did not carry the genocide of the Jews).
But, I would find hard to say the the Anti-Christ would use a calender over another. I do not remember that in the Bible.
Which calendar should I use?
The one people would understand.
Is it Scriptural if I worship by truth and in spirit alone, independent of time keeping, etc?
This verse his saying more the way the way we are to worship then on time keeping. Here is my two exegetical cents:
Seek the truth of God, get to know him who is spirit. So worship in is minimal sens is what consume the most of your toughs. So if you want to worship in truth and spirit. Seek that knowing, loving God be your default mode (what you do when you are idle). And by that you well be worshiping in truth and spirit.