[bug] sync times skewed with individual sync timers

[ghost]

• 70.0a1 (2019-08-27) (64-bit) (build 993cf82f6bbf09537f4cec8144cb69bfdf26bff3)
• Brief 2.6.0
• W10 Pro x_64 v1903 b18362.295

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  For quite some time had only a global sync period set (10 min), covering all feeds. Now, having set specific timers (hours | days) on some feeds the sync process times are totally skewed - sync being executed almost minutely.

[ghost]

Been able to reproduce this with FF 69 | 70 | 71, all x_64 on W10 Pro x_64 v1903 b18362.295.

Same global setting in each instance.

For consistency just changed just this one feed to an individual sync timer (min, hours, days did not matter and produced the same outcome).

The log is showing Brief going haywire with the sync schedule

[peteroupc]

See also #404 .