By the time I saw the job advertised it was already too late to apply.In this sentence 'too' is a/an -

• By the time I saw the job advertised it was already too late to apply.
- In this sentence 'too' is an- Adverb.

• too (adverb of degree)
English Meaning: to a higher degree than is desirable, permissible, or possible; excessively.
Bangla Meaning: অত্যন্ত বেশি পরিমাণে; প্রয়োজনের তুলনায় বেশি পরিমাণে।
- যেমন: He is too weak to walk.

• প্রশ্নে উল্লিখিত বাক্যে too, late এর পূর্বে বসে একে modify করছে।
- too সাধারণত adverb হিসেবেই বাক্যে ব্যবহৃত হয়।

Source:
1. Cambridge Dictionary.
2. Accessible Dictionary by Bangla Academy.