Improve NAV data refresh to twice a day

### Description
While most mutual funds' NAVs are updated in the API after midnight (post-AMFI release), some funds consistently get updated only after 9:15 AM IST. This creates inconsistency when querying NAVs early in the morning.

### Issue
- AMFI provides updated NAVs typically after 9:30 PM IST.
- Your API reflects these updates for most funds soon after midnight.
- However, certain funds INF879O01027 still show outdated NAVs until after 9:15 AM IST. ( I have this fund only but maybe still other too)

### Steps to Reproduce
1. Call the NAV API (e.g., `/nav/`) for various mutual funds between 6:00 AM and 9:00 AM IST.
2. Observe that some funds return previous day’s NAV, while others return current NAV.
3. Check AMFI’s published data — the updated NAV is already available.

### Expected Behavior
All funds’ NAVs should be updated in the API as soon as the AMFI updates are available — ideally by midnight or early morning.

### Actual Behavior
Some funds are delayed and only reflect the update after 9:15 AM IST.
AMFI link showing updated data: https://www.amfiindia.com/spages/


NAVAll.txt

### Impact
- Causes mismatches for automated systems, early-morning valuations, and alerts.
- Affects consistency and user trust in NAV timing.

Please confirm if this delay is by design or a bug.

Start by calling the /nav/ API between 6:00 and 9:00 AM IST and compare its results with AMFI's published data at https://www.amfiindia.com/spages/ and NAVAll.txt. Investigate how the refresh handles funds such as INF879O01027; done means the API consistently reflects available AMFI updates by midnight or early morning, or the delay is confirmed as intentional.

Written by the indexing model from the issue text.