偏偏 (מכל הדברים / חייב בדיוק עכשיו).

Rain arrives at the inconvenient moment

• You planned an outdoor event for the only free afternoon, and rain begins then.
• just had to偏偏piān piān这时候zhè shí hòuto rain下雨xià yǔ。 — The timing clashes with the speaker's plan.

Locate the pattern in real examples

• just had to偏偏piān piān (of all things / just had to): I我wǒtold让rànghim他tādon't别biégo去qù,him他tājust had to偏偏piān piāninsist要yàogo去qù。; early早zǎoto be not less than (a…不下bù xiàevening晚wǎnto be not less than (a…不下bù xià,just had to偏偏piān piān这时候zhè shí hòuto rain下雨xià yǔ。
• Read the whole clause before choosing a translation. The examples show the pattern in use; the context below determines what the speaker claims.

Follow the speaker

I我wǒtold让rànghim他tādon't别biégo去qù，he他tājust had to偏偏piān piāninsist要yàogo去qù。

• In the opening situation: just had to偏偏piān piān这时候zhè shí hòuto rain下雨xià yǔ。
• The timing clashes with the speaker's plan.

Check the limit of the explanation

• just had to偏偏piān piān also marks deliberate opposition, as in told让rànghim他tādon't别biégo去qù，him他tājust had to偏偏piān piāninsist要yàogo去qù.
• It does not itself identify whether the clash was accidental or intentional.

Repair the form before interpreting it

• The form to lean偏piān(completed / change)了leto lean偏piān这时候zhè shí hòuto rain下雨xià yǔ needs repair here. Write just had to偏偏piān piān这时候zhè shí hòuto rain下雨xià yǔ instead; keep the word or frame in its demonstrated order.
• Form and meaning are separate checks. After the repair, explain the sentence in its situation rather than treating a familiar translation as a universal rule.

Keep the distinction

Read the full reference: HSK 6 grammar — Adverbs.