Use Duration for const for delays

[cijothomas]

Addressing #2656 (comment)

[codecov]

Codecov Report

Attention: Patch coverage is 93.10345% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.2%. Comparing base (19dba69) to head (3b57d07).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/exporter/http/mod.rs	0.0%	1 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/mod.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2688     +/-   ##
=======================================
- Coverage   79.3%   79.2%   -0.1%     
=======================================
  Files        123     123             
  Lines      22601   22565     -36     
=======================================
- Hits       17925   17889     -36     
  Misses      4676    4676             

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