only 15 minutes after last session shown in calendar view

[SaptakS]

Fixes #3318

[codecov-io]

Codecov Report

Merging #3334 into development will decrease coverage by -0.11%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #3334      +/-   ##
===============================================
- Coverage        75.63%   75.53%   -0.11%     
===============================================
  Files              226      226              
  Lines            14923    14923              
===============================================
- Hits             11287    11272      -15     
- Misses            3636     3651      +15

Impacted Files	Coverage Δ
app/helpers/deployment/heroku.py	59.09% <0%> (-27.28%)	❌
app/views/super_admin/super_admin.py	71.42% <0%> (-12.5%)	❌
app/helpers/helpers.py	48.98% <0%> (-0.68%)	❌

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