Generally, there are around 4 periods of time covered in the first season:
Time 1: Yennefer's upbringing and training. This starts at the start of Episode 2
Time 2: Geralt's introduction at the start of Episode 1. This is probably around 30+ (could be 50) years after Time 1 and goes until Jaskier (Dandelion) is introduced. Estimate Jaskier to be around 20 at this time
Time 3: Geralt and Jaskier. This follows directly on from Time 2 and includes events like banquet in Cintra for Queen Calanthe (Episode 4) and then the events with both Geralt and Yennefer. This period lasts around 10-15 years until we get to Time 4.
Time 4: Ciri's timeline (current time). Starts with the fall of Cintra and ends with the big battle of Sodden Hill.